WEBVTT

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Rm 330: speaker?

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Rm 330: I think, you know, you know.

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Rm 330: what many of us have known Darrell for a long time. He's the professor in material science and engineering at Cornell. Before that, he was at Penn State. He is a pioneer in oxide MBE.

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Rm 330: And, also in str… you know.

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Rm 330: strain engineering of, you know, an epitaxial thin film, so that great knob that we learned to turn.

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Rm 330: And many other things I'm not gonna waste your time, talking about, because, I'm happy that he's here to talk about it himself. Thank you very much. Thanks, Karen. Thanks, Hugh.

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Rm 330: Thanks to you all for coming. It's been many years since I've been here at Rutgers, but I want to say that many of the great theoretical insights that I have gotten have come from… directly from Rutgers, and especially from my, former

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Rm 330: compatriot Craig Peeney.

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Rm 330: And I want to dedicate today's talk to Craig, who I'm sure that many of you

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Rm 330: know Craig and loved Craig, like, like I did. We started the same day at Cornell. Oh, wow. And,

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Rm 330: I was telling Karen how we both moved to Cornell, because we started, and his wife stayed in Chicago while he made the move, and my wife and kids stayed in State College while I moved. So the first year, we spent a lot of time.

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Rm 330: And today, I'd like to tell you, two stories that involve Craig at their, at their center, as she, as she looked at.

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Rm 330: Craig, as you know, Craig died in June.

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Rm 330: unexpectedly.

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Rm 330: This first story was published in July.

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Rm 330: The second story It was posted on the archive yesterday.

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Rm 330: Of course, both stories Craig knew fully about, because he was actually an active part of them, but I'm super proud to be here, and to honor Craig with this talk. Okay, so… so let's, let's get into the technical details.

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Rm 330: So, first of all, the collaborators that are involved in the work, first and foremost, Craig. You'll see a lot of theories. And then on the experimental side, it's my students, so Kevin, Rachel, and Megan.

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Rm 330: grew the films that I'll be talking about.

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Rm 330: They've all graduated.

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Rm 330: I'm gonna show some electron microscopy from my neighbor.

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Rm 330: David Muller, who's fantastic and also key to this work. And then various ideas you'll hear coming along in the talk. And the last important part has to do with the substrates that we use. And those are single crystals that are grown at the Institute for Crystal Growth in Germany.

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Rm 330: That made this, possible.

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Rm 330: And if you have questions along the way, I love questions, so please.

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Rm 330: Alright.

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Rm 330: the first.

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Rm 330: Maybe it's been 17 years since Craig Made this bold prediction.

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Rm 330: that, improper ferroelectrics, Should be able to scale down to the model air limit.

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Rm 330: And in Craig's words, this dependence…

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Rm 330: It's because they have a different primary order parameter, polarization, and it makes them more immune to depolarization fields.

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Rm 330: Because the electric polarization, which you need to have for electric, is preserved as long as the primary order parameter and the exact properties of something other than polarization is remaining stable.

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Rm 330: Darrell? Yeah? I'm taking up your invitation desk. Yeah, please. But just for context, can you remind us, what is the minimal thickness for a regular ferroelectric?

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Rm 330: Well, it varies, and some Farralectrics.

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Rm 330: today have been made in a single unit cell. So things like, hafnium oxide is one example, or hafnium plutonium oxide, yeah.

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Rm 330: Another example would be even bismuth ferrite, but it's with the right, mechanical and electrical boundary conditions, and that's untypical. So if I went… if I step back and said, let's talk about barium titanate, in barium titanate, it's several unit cells. So the… and this was motivated heavily by theory.

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Rm 330: So there was a famous prediction by…

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Rm 330: of VA and, 6 unit cells in very tight tanks, that motivated a lot of work to try to make ferroelectric thinner and thinner and see how thin it could be. Okay. It's this work from Craig that motivated us to look at improper ferroelectric and see how thin it could be.

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Rm 330: Okay, and what I want to… what I want to emphasize is that… and we weren't the only ones that were motivated by this, so I'll show you two other experimental groups who found that they could not get to a single unit cell.

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Rm 330: I'm going to show you a single formula unit, which in this case is half a unit 7. But if we look at the literature.

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Rm 330: This… this… this group is… this ETH group.

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Rm 330: So you can see it's… it involves Morgan Trustin on the growth side, Andre Fiebig for the SHG, Nicholas Baldin for Rafferty. And what they… what they see, and they look directly at the SHG, so they can… they can see as a function of temperature and foam thickness.

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Rm 330: Whether it's polar or nonpolar.

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Rm 330: But they see that below 3 unit cells.

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Rm 330: Which is 6 formula units. They no longer see any ferroelectricity at room temperature.

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Rm 330: FHG is second harmonic… Second harmonic generation. It's a way of seeing that the material, does not have a center of inverter, correct? So it's not, strictly, it doesn't…

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Rm 330: It's a necessary but insufficient proof for electricity.

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Rm 330: So, when they don't see it, it cannot be ferroelectric. There is no, spontaneous polarization to switch.

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Rm 330: But however, the temperature stopped at 300, so your problem with T3 is just lower than… Well, this is room temperature, this is room temperature. Yeah, it could be. It could be. They didn't make their… they did not make measurements to lower temperature. In this talk, I will show you a thousand Kelvin

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Rm 330: One formula unit is ferroelectric.

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Rm 330: Okay, just to jump to the chase. Improper photos, yeah. So, completely different than this. So… Can you just remind the idiots in the… which I include myself in the audience, the definitions of

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Rm 330: proper and improper, polar and nonpolar. Well, I'll try, but there are real experts in the room. So, the… the order parameter for a

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Rm 330: Copper farroelectric is polarization.

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Rm 330: An improper is something other than polarization. You see, in this case, it's a structural order parameter.

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Rm 330: And it might be called the Gamma 3 module?

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Rm 330: K3. It's K3. It's not a gamma. There's a reduction in crystal symmetry. It is. It drives the motorization. Correct. So that's coupled to it.

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Rm 330: is…

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Rm 330: is where the polarization comes in. So the one that I'm going to talk about is a trimerization of utrium manganese.

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Rm 330: which is the one that's… you see in this, if you're bringing it here. That's the one that Craig… Craig and,

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Rm 330: How I Seminar did this, this theory. This was your former student.

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Rm 330: Okay, so anyway, a lot of, a lot of, connections. So you're not worried about switchability for a ferroelectric, you're just saying it has to be polar? In… in… I am, to make it a real ferroelectric.

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Rm 330: And ours are switchable. So that's proper, improper, and polar, and non-polar and non-polar. So whether there's a… in the absence of an electric field.

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Rm 330: Is there a polarization in the material or not?

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Rm 330: So, if it's centrosymmetric, there can be no spontaneous polarization. Electric polarization. So, you're always talking about insulators for zero electrons. Yeah. So, the question is whether or not there's an electric polarization. Spontaneous electric polarization, zero electric field.

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Rm 330: would be a good example for electric. They have a spontaneous polarization, but it cannot be switched electrically before the material breaks in.

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Rm 330: Nicely. Nicely.

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Rm 330: So, you probably know, but if you take twisted boron nitride, you get domains that are ferroelectric and down, and they're only 2 atoms thick. So, would you consider that to be a ferroelectric?

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Rm 330: I would, I think it's called a sliding ferroelectric. That's right. And you could switch, right? Yeah, you could switch. With the electric field, actually.

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Rm 330: I mean, I think if you just do the twist.

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Rm 330: you get polarization that's kind of built in, and you can't then switch that with an external electric field. But if the external electric field can actually cause a sliding or something, then you can switch it.

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Rm 330: So, but it's not uniform, it is, you know, it's domain, and they can be switched with the… The pair electrics often are also not generally uniform, they have domains.

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Rm 330: Okay, thank you. Just to clarify, the old fare electric is Poland.

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Rm 330: Yes. But not all polar materials.

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Rm 330: are for electric. So it's a subset of polar. The ones that are nonpolar are pyroelectric only.

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Rm 330: Not Faroelectric.

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Rm 330: There's from the symmetry effect.

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Rm 330: Okay. Now, this isn't the only work that contradicts

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Rm 330: Craig's prediction over there on the right. There's… this was… this was in the material Gutierre Manganite.

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Rm 330: Another, you know, recent dish example is in the scandium Farhi, which is getting closer to what… I'm going to talk about TCM Farhi. I'm saying this all about these materials.

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Rm 330: But here's another… another example, and here they're showing, by electron refraction, there's a tripling of the unit cell. This is the trimerization that we're talking about. And they see when the films are thick, that if you…

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Rm 330: Danielle, if you can…

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Rm 330: If you can see where there's a streak here and here. So here to here, between… there's a tripling of the unit cell that is not present over here on the left. In fact, when the fills are thin.

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Rm 330: Or at high temperature, this is looking at a line profile across this pattern.

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Rm 330: there… if I look at the line profile here, where the film is thick, or at low temperature, can you see there's a little peak here? This tripling? There's a one-third and two-third peak here.

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Rm 330: Along the way. That's due to this tripling of the unit cell, that's the trimerization that shows that this, the unit cell is enlarged with this structural phase transition, and this drives polarization. This is…

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Rm 330: Okay, and that… that goes away when you, get… this… this red line is meant to distinguish between when you're either too hot.

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Rm 330: To have it. Or too thin.

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Rm 330: This is in-plane, but this polarization, are you talking about the polarization out of plane? Polarization is out of plane. The tripling of the unit cell is in-plane. E-plane. Yes. I see, there is the outer plane. I'll show the triple structure in just a second. A little bit subtle. It's, I mean, to be, the…

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Rm 330: it's a rumpling that happens in the crystal structure, and this… the rare earth, the scandium in this case, two of them will end up being upward and one is downward, and they're charged. So if you have two up and one down, you know, you're gonna now have a polarization that's out of plane in that direction.

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Rm 330: I'll show the crystal structure in a minute.

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Rm 330: But notice…

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Rm 330: Again, the thinness that's involved below 3 unit cells, no spontaneous polarization, much less the ability to switch it.

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Rm 330: So, in this… in this talk, and in our approach.

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Rm 330: We changed the mechanical and electrical boundary conditions.

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Rm 330: By changing the buffer layer and the substrate on which we group on.

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Rm 330: The previous examples were all grown, both grown on tuber draconia substrates, or sapphire.

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Rm 330: I'm going to show you this different, crystal next.

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Rm 330: Now, to get to Sean's point.

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Rm 330: This is the… Nonpolar material.

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Rm 330: So, and I want to emphasize how the rear Earth is this flat plane here. This is the out-of-plane direction, this is the in-plane direction. So, in the out-of-plane direction, there's a mirror plane here. If you have a mirror plane, you can't have a polarization, because that would…

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Rm 330: Be equal to its opposite, so there's zero polarization in the outer plane direction.

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Rm 330: In this structural, transition, 83.

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Rm 330: is what, is what, causes the, the trigonal bipyramids. This might look like an octahedra, it's not.

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Rm 330: It's a trigonal bipyramid, so it's got… the iron has 5 oxygens around it. There's a triangle in the plane, and then there's apicals.

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Rm 330: Okay, so if you…

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Rm 330: If you start to look at it, you can sort of see these are the three game plan options. This is the iron.

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Rm 330: And then these are the two apicals. So it's… it's a trigonal Viktor here, just so…

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Rm 330: Those, those start to… to… to pill.

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Rm 330: When they tilt, it causes… Need a go… sorry about that.

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Rm 330: It causes…

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Rm 330: A one up, two down, or if you switch… if you apply an electric field to it, it'll be two up, one down.

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Rm 330: So it's… everything's out of the plane. Clear on the structure now?

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Rm 330: Okay, now… What the, PTH group.

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Rm 330: suspected was going on in their lack of having, spontaneous polarization and for electricity to very thin films was that things were getting clamped to the substrate.

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Rm 330: And in theory, what Nicholas Falden's group was

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Rm 330: Physically clamped the very bottom of this

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Rm 330: In her case, Yiotrium manganine.

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Rm 330: to the cubic zirconia substrate.

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Rm 330: So, it starts off with these… Atriums being completely flat.

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Rm 330: And then…

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Rm 330: By first principles, she calculates, well, how does that evolve as a function of thickness? And you can see that it takes several formula units before you start to get this rumpling of negative treatment.

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Rm 330: So, the ETH group attributed clamping to the substrate as the reason that they couldn't scale down to the model near limits.

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Rm 330: You can see… here's the TFT calculations. This is what they see experimentally from their TDAM. So, what would the monolayer mean in this case?

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Rm 330: it would be one layer of rare earths, and one layer of… pyramids, or what? Well, that's what a monolayer would be. We find… we, that that half a unit cell, if you will, is unstable, and we actually need

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Rm 330: An iron oxide, a rare earth, and another iron oxide.

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Rm 330: So what I'm gonna show is… Polar, down to the… 3 quarters.

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Rm 330: Of a unit cell level, is this block here.

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Rm 330: And the unit cell is actually… 3 quarters. The unit cell is actually two. Two. Two, because of some structural defect. Correct. Exactly.

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Rm 330: Okay, excellent.

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Rm 330: Love it.

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Rm 330: All right, so… so first of all, you might say, well, those previous results, those were on insulating substrates, maybe you need to have some electrical boundary conditions by, providing some screening, even though, you know, Craig says you don't need to have screening.

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Rm 330: So we put it on platinum. We put it on iridium. Iridium. This is TEM data, this is cross-sectional TEM from David Muller's group. Down here, you see… you see the iridium.

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Rm 330: And you can see that the, the high Z layer here is the one that is, is brighter, okay? The low Z, if you have good eyes, between… this is now, in this case, lutetium here.

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Rm 330: There is a bunch of dots. Can we kill the light, though? Yeah.

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Rm 330: What are these down? That other one I guess. Yeah.

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Rm 330: Let's see what happens. Okay, go ahead. Darrell, sorry, I missed something. Why is it that electrical screening will help you with the structural defects? It won't.

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Rm 330: It won't.

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Rm 330: But we, we, we tried it. Oh, you just tried? We tried. In, in, in a, in a, in a, in a,

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Rm 330: proper referral electric, the electrical screening is very important. Okay. So we first wanted to see, you know, is this… as experimentalists, does this have something to do with electrical boundary conditions? And what we see is…

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Rm 330: You want to add more? Well, the basic picture is that when you develop an electric polarization.

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Rm 330: it will develop a depolarization field, because you put positive charge up here and negative… Oh, I see. So, if you can screen away that depolarization field, it's more likely you can get it to happen. Okay, I get it, thank you. And for proper ferroelectrics, that's… You don't need to do that. Right. For improper… You shouldn't need to do that. That was the research. Okay, thank you. So, in, in barium tightening, for example, and in proper ferroelectrics, you definitely

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Rm 330: want to do this, you want to get a standard part. Then I understand. It's a depolarization. So…

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Rm 330: Yeah, you can look to see with your eye, you can see this roughly, you can clearly see that there's one up, or two down, one up two down.

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Rm 330: Okay, but when you get down to the interface, this is iridium down here. This… this first layer that you see here of lutetium is pretty darn flat. And even the second one does not have the same rumpling amplitude, and you can see that in the data.

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Rm 330: See how it comes up and then it saturates?

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Rm 330: So it's not going to a formula unit or even a unit cell. We're seeing a very similar… it's not quite as low as…

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Rm 330: Here you see it in nanometers. The unit cell is about 1 nanometer, so this is about 2 unit cells. But does this mean that, let's say for… this occurs only one… along A direction, but for B direction.

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Rm 330: There's nothing like this? How do you… because for this, you know, just to this, through this. Yeah. For the D, for the B direction, if you call it B. So you want… you want to change your zone axis like this?

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Rm 330: So basically, this… so this happened also along… in depth direction? This one… Actually, the… Yes, yes, it does. Then, when you do the STM, they will all cancel up, down, up, down, up, down, up, down, zero. So we're seeing a… we're seeing a column, where the whole column is up. Yeah, so yeah, so up-down is up.

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Rm 330: Yeah, so all in this direction, basically, then that means, this is actually only… this occurs only in one direction, not the other direction.

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Rm 330: No, but the whole system retains three-fold symmetry. Oh, which is triangular. Out of every three atoms, two go up and one goes down. You don't have three-fold symmetry. Okay. And so, the PEM would look different if you came from 30 degrees. Correct. But the system, actually. I see, I see. One second. So, then one goes up and two goes down.

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Rm 330: why, C3 gets broke, right? No, no, it's not. No, out of every three…

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Rm 330: Every three… let's put it this way. Pick an atom and move that one up. The six around go down. Oh, I see. Yeah, I got it. So the axis is not in the center of the atomical.

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Rm 330: So it's happening through so-called strongerization, as Darrell says, because of the C3 is still there. But you have to look at strange angle, 30 degree angle, then you can see this. Yeah. That's awesome. You're in the right place. Terrible? Terrible.

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Rm 330: But still, they grow. It's so gross. Even on YSE, the lattice matching is not great. The films, it's a little bit hard for me to say, this is a metastable phase, so it's hard for me to know, and saying…

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Rm 330: As, it… this has not been formed in bulk.

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Rm 330: So Tsang has made a solid solution with yttrium.

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Rm 330: Utrium and lutetium? You're in the right place. So it's a little bit difficult to say how much lattice mismatch there is, because it's a metastable material that's never been made in bulk. Lutrium Farhana can grow pretty well. Yeah, yeah, yeah. It grows well on my SC, it grows well on my SE, yeah.

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Rm 330: And if we look… if we look, like, with a reciprocal space map and X-ray.

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Rm 330: It's not the same spacing as a substrate.

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Rm 330: Well, not the subject, but at least pitching these two. Pitching Uddin and Lutheran Iron Outside, pitching those. Even between those two, it's not a… it's not a,

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Rm 330: It's not perfect. It's like, it's… it's several percent. Several percent. We can see, we can see that we can… this is… this looks relaxed. Relaxed only. By x-ray, this looks like relaxed. When you do the glory, it gets relaxed right away, almost? We… the films that we've looked at by x-ray are not,

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Rm 330: By, by read… Read. By read… Yes. The resolution in read is not great.

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Rm 330: I, I would say… I have some coming up with, YSC.

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Rm 330: That's, like, 4%, and we can see that in reading.

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Rm 330: Yeah.

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Rm 330: I think there's no… I mean, if you ask me, I think it's relaxed from the get-go. Okay. So you use, ozone, or just notification? Ozone. Uddin?

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Rm 330: Uddium cannot be oxide? So we want to have 3 plus here on the iron. And we can grow it in 10% ozone, we can grow it… Yeah, but Uridium does not get oxide during the growth. Uddium just stays in the iridium? No, in terms of this? Yeah. Not seeing that in the image here.

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Rm 330: This is kind of irrelevant for the talk. We're gonna go to oxide. Okay, I just want to… in the terms of trivial… In terms of trivialness, in terms of trivialness, actually, in terms of trivialness,

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Rm 330: Yeah, so we… we see the same problem. It does not go down to the single unit… it doesn't go less than a couple unit cells when we grow on either cubic zirconia or iridium, which is not… which is in agreement with… and it's… it's…

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Rm 330: It's slightly… it's slightly better on Iridium in terms of the amplitude. This thing not being flat. You can see that on Iridium, it's a little bit more puckered, but it's not to the bulk value.

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Rm 330: Until several formula units. Okay.

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Rm 330: No.

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Rm 330: Let's look… take a top view of what's going on here.

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Rm 330: This… so here, we're looking… we're looking down on the crystal structure.

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Rm 330: And the… Trimerization happens along this diagonal of the unit cell.

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Rm 330: The paraelectric phase, the one that has no trimerization, I've outlined your ingredient. Here, this is… this one has the tripling.

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Rm 330: And if we look at the substrates that people have been growing this on.

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Rm 330: Cubic zirconia, 111 cubic zirconia, 111 iridium, 111 Platinum, okay, there's different things people have tried. Notice, this…

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Rm 330: Is well matched to the phase that we don't want.

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Rm 330: We want this.

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Rm 330: Okay, so you might think from, from, just from a lattice, perspective.

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Rm 330: You're trying to… we want to epitaxally stabilize that.

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Rm 330: We don't want to stabilize the non-ferroelectric one.

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Rm 330: And it's even worse if you look at it from the side. So here's the top view I just showed you. What we want from the side is we want this puckering thing. We want the two down, one up, two down, one up thing.

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Rm 330: If I look at YSD from the side, it's flat!

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Rm 330: If I look at, I think I have,

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Rm 330: Okay, the same thing's true with iridium and platinum. They're all flat from the side, okay? So, if you want this thing to be puckered.

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Rm 330: you want to have something that has puckering in the substrate. We normally think about lattice match as just a two-dimensional thing. We don't think about puckering, we don't think of the out-of-plane direction.

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Rm 330: But we really want to stabilize this. We want a bigger unit cell, and we want it to be puckered. And that's the key to changing the mechanical boundary ignition that I'm about to show you. Does the… does the puckering break the symmetry? It does, it triples. So then you're just applying a field to a system

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Rm 330: It's like, if I apply a magnetic field to copper, it becomes ferromagnetic. Yeah, yeah. That doesn't prove copper is a ferromagnet. In the absence of the substrate.

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Rm 330: But in the presence of the substrate, it is.

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Rm 330: So we could…

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Rm 330: Maybe you're one of our reviewers. But it depends on the boundary conditions. No, but the question is, is it going to be reversible? Because if the substrate, you know, in Pierce's analogy, if the substrate…

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Rm 330: imposes a certain direction of polarization, then you wouldn't expect it to be reversible. So it is reversible with electric field, but not… I mean, experimentally, this is where the PFM comes in. I'm not going to show you the PFM, but experimentally, not down to the 3 quarters of a even cell.

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Rm 330: piezo force microscopy. Sorry, I, I don't… Somewhere, somewhere in here. There he is. There are ways to do that with intercalation. We have not, we have not, we have not tried. It, it's,

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Rm 330: This stuff… this stuff doesn't… doesn't cleave like that, so it's not a… it's not 2D, it's a layered material. But maybe intercalation? Maybe. And in such a… in such a case, I think that it could be that Craig should be right.

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Rm 330: But it's difficult to do experimentally.

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Rm 330: But these do switch, and they switch down to, I think it's…

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Rm 330: three unit cells that we've shown that are collaborators by PFM, so electrical switching.

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Rm 330: Awesome. Even though it's biased by this underlying set. I see. So, but it has a preferred permutation, as well. There's… well, these two states are not equal.

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Rm 330: Energetically, right? We… then it's three layers on it.

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Rm 330: Prevent sin.

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Rm 330: when it's thin, the two… I would agree with that. I would agree with that, yeah. So you might… you might expect back switching when you… but it doesn't… the… so our PFM collaborators were able to switch it, and

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Rm 330: And down to this thickness limit, they tried thinner, but down to the thickness unit of a few unit of cells, it did not back stretch.

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Rm 330: But it could be that the bias due to the bias. And their measurements are…

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Rm 330: So that, when you switch it, that means you've created a domain wall right locally. Locally, yes, yes. And not in this talk, but we have a PRL seeing domain walls. So they've been, like, there are… they do have domain walls.

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Rm 330: Yeah. Saying it's been going well with these materials for

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Rm 330: All right, same thing is true, not just for YSE, it's also true for iridium. So here in the iridium case, if we look at it from the side… if we do it from the side, see how this is also totally flat?

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Rm 330: Right.

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Rm 330: There is hope, though. If you… if we look to the literature of what people have done, there was this beautiful

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Rm 330: Russian order.

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Rm 330: We're… They made films.

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Rm 330: You might call them bad films. Of lutetium ferrite, And…

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Rm 330: they… they were… they were, so far off composition in their film that they got second phase of this spinel, Fe304, magnetite growing in the film. And interestingly, that spinel phase doesn't come as, you know, round precipitates, it comes as planes.

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Rm 330: these planes that have these black arrows here in the film. So, there's planes of MP304, and then there's a single phase of the hexagonal Lutetium ferrite, or lut… they're not deliberately doing this, it's not trying to make a super lattice or something. They're just off composition, and they get these planes.

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Rm 330: And what's interesting is when they… when they use electron microscopy to look at the interface between the spinel phase and the lutetium ferrite.

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Rm 330: They see, and they have a model over here on the right, and this is directly from their paper. It's not, you know, it's not… it's old electron microscopy, it's not near the resolution of the work that I'm showing you in the top.

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Rm 330: But… and you see this unusual layer here that has two lutetiums in a row and an iron.

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Rm 330: That's what they call this reconstructed interface. It's got these two lutetiums and an iron, these two lutetiums and an iron. Notice it's not flat.

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Rm 330: That is present between

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Rm 330: this lutetium ferrite. In the lutetium ferrite, you can see that there's some… some, huckering in the lutetiums, very close to this phenolph.

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Rm 330: Now, if we look at the model, maybe it's more clear over here from their TEM. This, this is… this is their actual data, but what they extracted from it, and we're in full agreement with what they, with what they claim.

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Rm 330: that what they claimed was in the Lutetium Farre, Right next to the spinel.

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Rm 330: It's one up, two down, one up, two down, that this thing has puckered.

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Rm 330: Not 3 unit cells away.

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Rm 330: This gave us hope

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Rm 330: that by using this kind of a transition structure, which they call a reconstructed interface, I'll call it a bridging layer.

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Rm 330: That we could go from… a substrate.

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Rm 330: to Parker Lutzium ferrite, and maintain the electricity. So this, C, TMD is absolutely beautiful, but I'm a little confused. Yeah. So, top layer, if you see more or less, left-hand side.

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Rm 330: Up here? Yeah, so around there, I see Ooved now. Yeah.

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Rm 330: And also, Israel is down, now, now. Yeah, that's correct. It's kind of mixed. Well, I would say that there's a domain wall. So, so this, this, the polarization is that way.

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Rm 330: Here, the polarization is that way. You mean the bottom part is,

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Rm 330: This, this… this… well, here, I think it's pretty clear. It's two ups and one down. Okay. I think that's what it is. But the, like, you know, it's… it's not my fault, it's not my, my image, but…

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Rm 330: The part that I want to point out is that there's hope. There's hope. This thing has gone from this spinel structure.

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Rm 330: Which is not polar. Right.

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Rm 330: To this polar structure, where this puckering happens very close to the spinel.

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Rm 330: And it's true on both sides. And on both sides, you see this 2-lutetium iron, 2-lutetium iron, as the… as the layer that nature chose.

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Rm 330: They just had too much iron in their sample.

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Rm 330: it forms this… it precipitates out this plane of F3 and 4. Nature chooses this interface, this… this bridge between the spinal structure and the underlying improper paroleelectric. So is this… is this lattice matched now?

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Rm 330: No, it looks coherent. Is it not coherent? The last… E is coherent.

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Rm 330: That is.

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Rm 330: The bulk lattice constant of this material is a few percent different from this.

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Rm 330: I don't know, in this field of view, what's going on. Okay. We have not… I've not analyzed it, David. Okay, so Darrell… what I wanted to say was this, right? So, Hope Vision looks like a countdown fall.

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Rm 330: down the surface where I built, like,

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Rm 330: So there is a… Over, down. Down region is a down, down, up. That's what I see. It's more or less down, down, up. It's not 100% clear. Yeah, yeah, I agree. I agree, right? So, and I think I mentioned this some years ago, I think this tendency is probably due to

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Rm 330: some kind of an auction, or… Yeah, yeah, you did. Some auction content. This, this material can conduct, this can connect. There's a projection always want to be either this one or that one. It's an auction kind of maintenance issue. Could be, could be. This material…

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Rm 330: So this, there can be some screening going on there? Because for iron is 2 plus there. Actually, iron is 2+.

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Rm 330: in spinner, compared with that 113… I agree. I agree. It's a mixture of 2 plus… It's a mixture of 2 plus and 3+, which is responsible for the conductivity. I think that that could be important for screening and allowing, you know, head-to-head is normally a high-energy configuration. Okay, I agree.

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Rm 330: But for the purposes of this talk, this is what gave us hope, this is experimental. And before I drag you through the crystallographic details of how we did it, I wanted to show you that it works.

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Rm 330: So, this is now, you know, David Mueller resolution.

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Rm 330: This is… this is the artificial structure that we've grown.

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Rm 330: This has a non-centrosymmetric substrate, non-centrosymmetric buffer layer.

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Rm 330: But on top of it, what I hope you can see, Is that this lutetium layer

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Rm 330: Which is the first Lutisian Larry's puckeard. Here's a blow-up on it.

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Rm 330: And in fact, the magnitude of that puckering is quite similar to what I showed you was happening in the bulk of the films.

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Rm 330: And it's right on top of this transition layer.

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Rm 330: Okay, so I just want to show you, first of all, it works, before I drag you through the details of how we got there. Is that assertiveness, or is there something on top?

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Rm 330: This is a surplus. Yeah. So this is…

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Rm 330: we call it the… in the paper, this is, like, the final result. I'm just… it's like a preview, okay? Can we scale this down? And if you look… if you look closely.

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Rm 330: you'll see that there's iron on the top, and iron on the bottom, and just one lutetium. So it's 3 quarters

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Rm 330: Of a unit cell.

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Rm 330: or one and a half formula units, I don't like to count. There's one lutetium layer.

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Rm 330: Okay.

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Rm 330: So, formula is now 113. What is the right formula for that?

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Rm 330: Well, it's got an iron oxide on the top of it, and an iron oxide underneath.

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Rm 330: So it's like a rotation 1, IL3?

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Rm 330: Well, I am cool, maybe.

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Rm 330: If I am too old or something, I think so.

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Rm 330: I don't know exactly how many oxygens there are.

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Rm 330: So, but there's a 2 to 1 ratio, 2 to 1 ratio between iron and logicia. That part… It's pretty exposed to air. Right at the interface, which is a little tilted, those two, slightly tilted, right at the interfacial layer.

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Rm 330: It was two… the one. No, below. Yeah, it was two. The last two were lutetiums. See these two lithiums? Yeah, the lutetiums. Lutetium, lutetium iron. I see. That is the magic. See? Lutetium, lutetium iron. It's this thing. It's this thing that Mother Nature forms.

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Rm 330: We have duplicated it. We have copied Mother Nature to make it so that we can transition from the substrate

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Rm 330: To an improper ferroelectric that retains that spontaneous polarization to the monolayer limit.

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Rm 330: Okay, okay, and here, now this is the whole structure. The whole structure starts with this new single crystal substrate, call it SGMZ.

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Rm 330: Okay, I'll tell you the full on the board, but it's strontium, gallium, magnesium, zirconium oxide.

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Rm 330: The stuff is grown by Jaikowsky.

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Rm 330: On top of it is the bottom electrode, that's strontium, cobalt, ruthenium oxide, okay? It's no longer, no longer… What? How is that buffer layer grown? MB, MB. Is that the entire composition? MB. This is the entire composition! 1, 2, 4? 1, 2, 4. Absorption control. 1 to 4. Yes! This is the right audience, you guys are…

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Rm 330: Okay, now, and then on top of this, we do this deliberate bridge that nature wants, and then put down this

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Rm 330: Formula and a half unit.

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Rm 330: Of the product or good time. Okay.

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Rm 330: So now can you say if it's correct, look correct. That must be correct.

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Rm 330: Oh, that one is coherent, yeah, and we have an RSM on it, yeah.

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Rm 330: So, since you gave us the ending, I wanted to ask, was Craig right? You didn't need to worry about the depolarization field? There's no… Of course, Craig, sorry. That's my thought. Oh, no worries. You didn't emphasize that just now.

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Rm 330: But there's no screening with this, right? Good. I just wanted to… So we've added a metal.

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Rm 330: Oh, so you did that? This is a metal. Okay. We wanted to be able to actually test, not just that it's polar, but that it can be switched. Oh, good. So we need a bottom electrode. Okay. That's why we added this metal.

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Rm 330: We have not tried, the same approach with an insulator and a bridging layer to see if it buckers. Okay, that's what I want you to do. Okay. Okay, fair enough. And just to… I showed you the same plot over here of how we go from completely flat lutetian layers

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Rm 330: And eventually they get their standards basic, but look right from the get-go on what we call this, bridging layer engineered template.

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Rm 330: The thing's puckered.

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Rm 330: That's the beauty, that's this one over here. So I showed you these two, these two before. These two before, the first lutetium layer is nowhere near as puckered as the steady-state value. Same thing here, okay.

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Rm 330: This… this is our… these are our gross. I… I… these are our gross on a video, our gross on cubic, our gross on this… this bridge… bridging layer, just like I showed you before. Here's the transit… the bridge right here, and here you're seeing this thing is fully puckered, which is what you see over here from the puck layer, puckering in.

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Rm 330: Alright, now I try to get to the details.

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Rm 330: Well, our strategy is to lattice match

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Rm 330: To this one. And an out-of-playing partner.

294
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Rm 330: So we want a unit cell that's the same size as that.

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Rm 330: this material, which was suggested by Bob Cava.

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Rm 330: Has the same size in itself.

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Rm 330: That's… so that's how it differs.

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Rm 330: Now…

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Rm 330: And this came out at a more meeting, Sean. You may have been there. I was bemoaning the fact that we were trying to do this, and I asked Bob if he knew of any conducting

300
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Rm 330: hexagonal ferrites. And he said, oh yeah, of course.

301
00:40:36.890 --> 00:40:57.449
Rm 330: strontium, cobalt, you know, all that. Oh, yeah. Jet GPT! Everybody gets it, everyone gets to it, you know? And he's like, oh, and also bury him. Bury him, cobalt, radium.

302
00:40:57.450 --> 00:41:11.599
Rm 330: And, and I said, oh, where do I find that? He said, like, I just wrote a review paper. Go look at my review paper. We did, there it was, okay. And, and this is, what, well, actually, Bob had made, had made this material, Sean

303
00:41:11.600 --> 00:41:18.090
Rm 330: And the Rutgers guy at Ong, had measured its connectivity in powder form, but another group had made a single crystals of this.

304
00:41:18.560 --> 00:41:25.430
Rm 330: our films actually conduct even better. So this… the films I'm showing you, they're epitaxial, It's the right structure.

305
00:41:25.580 --> 00:41:26.270
Rm 330: It's good.

306
00:41:26.550 --> 00:41:32.939
Rm 330: Okay, now, the… that's the… that's the conducting bottom electrode.

307
00:41:33.170 --> 00:41:34.919
Rm 330: This is the substrate over here.

308
00:41:35.520 --> 00:41:44.070
Rm 330: So, this is Bob's conducting bottom electrode that has a nice, you know, in-plane lattice match.

309
00:41:45.330 --> 00:41:48.630
Rm 330: to the struct… to the… to the GCM ferrite that we want.

310
00:41:48.740 --> 00:41:53.950
Rm 330: Now, just to show you the structural elements, these… hexagonal,

311
00:41:55.380 --> 00:42:01.799
Rm 330: This is a magnetoplumbite, magnetoplumbite structure. But all of these hexagonal ferrites

312
00:42:01.940 --> 00:42:13.700
Rm 330: You can think of as superlattices between different blocks, and this was noticed, you know, by the Phillips people in the 1950s. And just to see the same blocks that are active here, here you see the coordination polyhedra involved.

313
00:42:13.880 --> 00:42:20.389
Rm 330: the… Iron in this trigonal bipyramid is right here. It's in the so-called R-block.

314
00:42:20.580 --> 00:42:39.190
Rm 330: And then separating this… this R block can be a spinel block, which is called the S layer. And the S layer consists of these different, octahedra, like you see, like, here. And that S layer is made of alternating A and B layers. Okay, so there's a whole… a whole,

315
00:42:39.930 --> 00:42:43.130
Rm 330: the whole nomenclature for this, okay? So…

316
00:42:43.480 --> 00:42:57.969
Rm 330: you may or may not… the… some of you may have seen these things from Philips, and these… these… the way you can build up these different structures, but it's all… it's all based… this is… this is spinel, over here, which is based on this A layer and the B layer.

317
00:42:57.970 --> 00:43:07.069
Rm 330: Those contain octahedra and tetrahedra. Okay, like you pointed out, there's IR2 plus and IR3 plus going on there.

318
00:43:07.070 --> 00:43:20.090
Rm 330: This R block is where these trigonal bipyramid… pyramids are, just like in the trigonal bite pyramids that are in the lutetium Farhrite structure. There are structural similarities between this stuff and the improper ferroelectric will want to put on top of it.

319
00:43:20.660 --> 00:43:28.349
Rm 330: Now, if we… if we look at our… our strategy here, we have to think, how is it that we're going to put these things together?

320
00:43:28.880 --> 00:43:30.770
Rm 330: So we have a substrate.

321
00:43:30.990 --> 00:43:34.029
Rm 330: that has alternating R and S blocks.

322
00:43:34.470 --> 00:43:37.169
Rm 330: And on top of that, we want to put this bottom electro.

323
00:43:37.520 --> 00:43:50.470
Rm 330: So, what we… what our strategy is, is to look for a common layer. And that common layer is this so-called B layer. You can see how I drew this to end with this B layer.

324
00:43:50.490 --> 00:44:03.019
Rm 330: And then choose this one to start with the B layer. So the obvious way to put these two together is you have this B layer be that B layer, and that's the way we put this interface together. So in growing it, you know, we're happily growing these materials.

325
00:44:03.270 --> 00:44:12.150
Rm 330: And deliberately make the transition at the right spot. And the obvious place to make that transition is with the B layer, to go from this

326
00:44:12.550 --> 00:44:19.730
Rm 330: M-type hexaferrite, to, Bob Cava's exopherite is conducting quantum electric.

327
00:44:20.290 --> 00:44:24.590
Rm 330: Okay, so that's one interface. The next interface is to go from the bottom electrodes

328
00:44:24.740 --> 00:44:28.559
Rm 330: Through the bridging layer into the lutetium fairing.

329
00:44:28.740 --> 00:44:34.379
Rm 330: And I know this is complicated, so I wanted to show you that, first of all, it just works. I don't bore you.

330
00:44:34.620 --> 00:44:50.609
Rm 330: The details of this are to copy Mother Nature. So this is… this is what the Russians showed to work, that you can go from spinel, which is this alternating A and B layers that I've shown you.

331
00:44:50.920 --> 00:44:54.040
Rm 330: To the… Lutetium.

332
00:44:54.210 --> 00:44:55.130
Rm 330: Fair rate.

333
00:44:55.660 --> 00:44:57.800
Rm 330: Freighton.

334
00:44:58.050 --> 00:45:07.330
Rm 330: via this layer that has two lentiums and one iron. That's this… that's this layer here. It's a… it's very related to the A layer, so you can see that this is, you know, happily going.

335
00:45:07.410 --> 00:45:23.679
Rm 330: B, A, B, this is where the A layer would be. And that layer is the perfect one to make the transition to the hexagonal vertex. So that's exactly, you know, following this advice of how you go from this finale to here, it's with this bridging layer.

336
00:45:23.710 --> 00:45:31.050
Rm 330: So that's what… that's the strategy that, that we… that we did. So we're not growing on this spinel.

337
00:45:31.500 --> 00:45:44.129
Rm 330: But we are growing with a structure that has B layers, like a spinel has, and then we want to go to this A layer, where we're going to use this special kind of A layer that has two lutetiums and 1 iron, and then go to the

338
00:45:44.240 --> 00:45:56.109
Rm 330: Leticia and Farhin on top of it. Okay, I've shown things as, you know, cartoons that fit together, but I think you can get the strategy. We're trying to chemically follow, you know, the way that Mother Nature wants to put these things together.

339
00:45:56.110 --> 00:46:01.880
Rm 330: Substrate is sort of all 9 inches wide, so substrate, your stoichiometry?

340
00:46:01.880 --> 00:46:16.939
Rm 330: Right, the number is 1.0-something, all those… Right, okay. Why is it all non-H2 numbers? This thing, this thing here. Yeah, 1.03, is it intended, or what? Totally intended. Huh? So, so, strontium, this is very… it's almost strontium hexagonalate.

341
00:46:16.940 --> 00:46:17.730
Rm 330: Almost.

342
00:46:18.520 --> 00:46:27.739
Rm 330: So, the stuff that sticks to your refrigerator, the refrigerator magnet, the M-type hexaferrite, is barium FE12019.

343
00:46:27.940 --> 00:46:45.769
Rm 330: This stuff is almost strontium GA12O19. Oh, 11. Well, it's only 11, okay. And the reason is that strontium hexagallate does not melt congruently. And so the trick the crystal growers use, in trying to do Tchaikovsky, you need to have something that melts congruently.

344
00:46:45.890 --> 00:46:48.860
Rm 330: The trick is that instead of having

345
00:46:49.070 --> 00:46:56.819
Rm 330: 12 galliums there. You make a half of magnesium and half of zirconium.

346
00:46:57.020 --> 00:47:03.249
Rm 330: And by doing this trick, it makes it so that this mixture now melts congruently, and it's possible to pull a single crystal.

347
00:47:03.550 --> 00:47:18.740
Rm 330: So this is a nice single crystal substrate on which we can grow. I mean, when you're doing… I don't know if you're maybe bulk crystal. Same. It's sane, okay. When you're trying to make… when you're trying to make a bulk crystal, it's much easier to grow it. It melts congruently.

348
00:47:19.230 --> 00:47:34.880
Rm 330: So that's… that's why… I probably have some crazy composition. The stratomy is varied, and somehow it is not… no position is clean, you always have some mixing of something every day. So this is based on ICC analysis.

349
00:47:35.060 --> 00:47:50.849
Rm 330: So this is… they grow a crystal, but I tried to explain the general idea. The general idea is strontium hexagonalate and make it possible to grow the crystal by, making it melt your growth. And it's an insulated? Insulated. You can see that it's this intrusive growth. It's yellow.

350
00:47:52.170 --> 00:47:52.990
Rm 330: Alright.

351
00:47:53.440 --> 00:47:56.900
Rm 330: Okay, so I showed you it worked. This is now the whole stack.

352
00:47:57.030 --> 00:48:03.170
Rm 330: Just so you can see, you know, I showed you the cartoons before at every point. It agrees really well with David's data.

353
00:48:03.790 --> 00:48:14.929
Rm 330: termination of the substrate is clean, you have just single, well-defined termination layer? Automatically? As you grow? Or you have to… We worked out a,

354
00:48:15.120 --> 00:48:27.459
Rm 330: an etch and a kneel step, to get the… and I'll show you some steps in just a second. Yeah, okay. There's a lot of details, a lot of detail. We worked really hard on this, okay? And Craig… Craig was instrumental, because Craig was like, this can't be!

355
00:48:27.730 --> 00:48:31.610
Rm 330: I know this has got to be stable down to the monolayer limit.

356
00:48:32.200 --> 00:48:46.319
Rm 330: So you guys need to fix your experiment. I don't know if other theorists in the room have the same opinion sometimes of experiments. All right, now I wanted to look at the epitaxy from the side.

357
00:48:46.740 --> 00:48:56.029
Rm 330: So this… we've seen the top view, but if we look at the side view of what we want, it's got this two down, one-up motif.

358
00:48:56.410 --> 00:49:06.290
Rm 330: And if we look at the, at the Bobcata's buffer layer, along the same direction, it's lutetium, lutetium iron. Notice, it's not flat.

359
00:49:06.690 --> 00:49:07.770
Rm 330: It's not flat.

360
00:49:08.790 --> 00:49:14.489
Rm 330: And to Pierce's point, it might put a slight bias on it, but we can switch them back up.

361
00:49:15.870 --> 00:49:23.860
Rm 330: So it's, it's, it's different than just in-plane lattice matching. We have some bunkiness going on as well, and I, I, I, I,

362
00:49:24.750 --> 00:49:31.439
Rm 330: So just, you know, to contrast that, you know, before, you know, Iridium was flat, our stuff is not flat. Now.

363
00:49:31.800 --> 00:49:40.370
Rm 330: During growth, you can actually see the trimerization come about. I showed you early on, you know, using second harmonic generation and also electron diffraction to see that trimerization.

364
00:49:40.580 --> 00:49:44.480
Rm 330: I'm going to show you that the stuff is trimerized to a thousand Kelvin.

365
00:49:44.660 --> 00:49:46.700
Rm 330: All the way to the one model ever.

366
00:49:47.910 --> 00:50:01.310
Rm 330: Which is different from the clamp case. So if you're on a substrate that is not, like our special substrate, like you're on YAC or something, you don't see the trimerization going on. Here, in electron diffraction, when you're either thick enough.

367
00:50:02.420 --> 00:50:06.189
Rm 330: When you're below the transition temperature, you see this hybridization.

368
00:50:07.040 --> 00:50:10.029
Rm 330: Now let's look at it as a function of temperature.

369
00:50:10.630 --> 00:50:29.240
Rm 330: for the growth sequence. So this is starting at the bottom electrode, so Bob's bottom electrode. You can see it's got a unit cell that has, this bigger extent in plane. It's the same extent as this trimerization, but the intensities are quite different. So you can spot, you know, the hexagonal plutetium Farray.

370
00:50:29.240 --> 00:50:34.949
Rm 330: as this clear, tripling here. This one, the intensities are different, but it's also…

371
00:50:35.890 --> 00:50:37.530
Rm 330: Then we put the bridging layer on.

372
00:50:39.230 --> 00:50:44.870
Rm 330: Here, here, this is just the one and a half formula units. You see the clear, clear trip blink? Notice the temperature.

373
00:50:45.150 --> 00:50:49.289
Rm 330: So this is not just a 1000 caliber, it's almost 1,200 caliber.

374
00:50:49.870 --> 00:50:51.470
Rm 330: Rim temperature, still there.

375
00:50:52.460 --> 00:51:11.850
Rm 330: If we do the, you know, the side… side view of this thing, you can see that… that as the structure evolves, and you do… you do… you do see that the intensities of these… of these peaks are different from Bob's conducting layer versus the eventual latissim Farh.

376
00:51:12.670 --> 00:51:26.139
Rm 330: Anyway, I just wanted to say, the trimerization, you can see that it's hot and present. So, totally unlike the clamped case, in the thin film case, the, down to the single monolayer, we see this fairly nice. Okay, I showed you this.

377
00:51:26.930 --> 00:51:44.170
Rm 330: It is not absorption control for that particular URL search. Generally, particular layer. Lutetium ferret is not absorption. Bob Kalis layer is absorption controlled with the radii. Now, because Sean's here, I thought I'd show you the, the AFMs.

378
00:51:44.210 --> 00:51:48.430
Rm 330: So, this is what our… these are step-in tariffs.

379
00:51:48.610 --> 00:51:55.820
Rm 330: So… is the substrate with this bottom electric. This is the, 1.5 formula units on top of it.

380
00:51:56.070 --> 00:52:15.470
Rm 330: So the… the… I mean, it looks like… looks like you're felt. I mean, these things are nice step and terrace, structures. Each element. It's got… I mean, my students worked hard. Students worked very hard on this. Are those, is, are those single domains? Is each step a different domain?

381
00:52:16.030 --> 00:52:27.389
Rm 330: I couldn't… I couldn't see that. I don't have the res… I don't have the ability to see that. By… by TE… by cross-sectional TEM, we can see if it's a single domain. Here, we're just seeing the… the height of the staff.

382
00:52:27.570 --> 00:52:38.470
Rm 330: So, I can't see that the two upper, one down, or two down or one up, I can't see that resolution. I can just see that it has these, formula… charge neutral formula units.

383
00:52:39.210 --> 00:52:42.990
Rm 330: But from a growth perspective, it's important for growers. Okay, so I know Sean…

384
00:52:43.140 --> 00:52:57.120
Rm 330: This case also probably there is preferred prioritization orientation because of… I believe there is. We have not seen domain walls. They have to come in from the PFM, but what we see has grown in one direction.

385
00:52:57.850 --> 00:53:03.699
Rm 330: Okay, it also works on sapphire, so I, you know, I dragged you through this obscure substrate.

386
00:53:03.830 --> 00:53:05.030
Rm 330: What are the other time?

387
00:53:06.800 --> 00:53:08.349
Rm 330: Can we start at, 12.

388
00:53:12.110 --> 00:53:13.030
Rm 330: I'm sorry.

389
00:53:13.190 --> 00:53:20.720
Rm 330: Okay, it works on Sapphire, but the films are not nowhere near as fiscal.

390
00:53:20.950 --> 00:53:30.999
Rm 330: Maybe that's a good place to stop. I'll say on the second one. Right, on time? 5 minutes. 5 minutes? Okay, I can give you… okay, let me give you the 5-minute version.

391
00:53:32.230 --> 00:53:36.789
Rm 330: Okay, so, so, Craig thinks it's true, these are also correct words.

392
00:53:37.050 --> 00:53:41.000
Rm 330: He thinks it's true not only in this geometric and proper for electric, but then…

393
00:53:41.220 --> 00:53:44.849
Rm 330: to be true for all proper parallelings. Maybe even both.

394
00:53:46.210 --> 00:53:50.830
Rm 330: Second half of the talk. In 3 minutes. In 3 minutes.

395
00:53:50.880 --> 00:53:58.970
Rm 330: Okay, so, remember the material that sticks to your refrigerator? Very hexaferrite? Okay. That, that material.

396
00:53:58.970 --> 00:54:17.560
Rm 330: is on the verge of a ferroelectric transition, and that was pointed out by many people. I just want to, you know, point out Tim Scott, and when I saw this, I thought, wow, here's a very strong room temperature ferry magnet, a 60 refrigerator, that's on the verge of a ferroelectric transition. Maybe with strain, we can push this thing over the edge and have a room temperature

397
00:54:17.560 --> 00:54:19.129
Rm 330: For electric front, maybe.

398
00:54:19.470 --> 00:54:31.969
Rm 330: Okay, in bulk, what happens? This is the crystal structure, complicated. Same structure I showed you just a second ago, so it's trigonal bipyramids. The iron in that trigonal bipyramid is not in the center.

399
00:54:32.200 --> 00:54:41.410
Rm 330: It's oscillating back and forth, slightly below, slightly above, okay? It lives in a quantum well where it can tunnel.

400
00:54:41.410 --> 00:54:54.099
Rm 330: So there's not much of a barrier. Something back and forth, and at room temperature, it's, 6mm, okay? So, like, like saying, told me this morning, that what, you know, what we're trying to do here is impossible, okay? But with strain.

401
00:54:54.260 --> 00:55:03.119
Rm 330: We can make it so that the… this double well is a little bit further apart, and we can start to… so that's the… that's the concept.

402
00:55:03.230 --> 00:55:06.489
Rm 330: Now, the idea is, is not, original.

403
00:55:06.670 --> 00:55:15.449
Rm 330: the… this… this was pointed out, if you guys know, he was a visiting scientist with Lauren Bleach.

404
00:55:16.260 --> 00:55:21.970
Rm 330: He predicted that if you put about 4% strain

405
00:55:22.310 --> 00:55:26.590
Rm 330: By axial compression of the material, it should become ferroelectric.

406
00:55:28.070 --> 00:55:38.369
Rm 330: What he didn't predict, and what Craig predicted, was… was, and experimentally, 4% for… that's a lot of strains. No way we're gonna get there. But what Craig predicted.

407
00:55:38.510 --> 00:55:45.959
Rm 330: was that interesting things happen even before you get… and Crick Group's 5% strength, so it's more challenging.

408
00:55:46.230 --> 00:55:49.249
Rm 330: But even before you get there, I'm going to show you the results at 1% strength.

409
00:55:50.070 --> 00:55:56.080
Rm 330: That this thing should… Start to have

410
00:55:56.560 --> 00:56:02.139
Rm 330: domains, these nanopolar domains in the plane.

411
00:56:02.310 --> 00:56:13.329
Rm 330: And that's what's shown by the energies here. So, you can see that the high energy stuff is looking at what's happening

412
00:56:13.460 --> 00:56:15.319
Rm 330: From one layer to the next layer.

413
00:56:15.480 --> 00:56:18.949
Rm 330: Here, side by side, we're looking at what's happening in the same layer.

414
00:56:19.050 --> 00:56:24.060
Rm 330: And so, in the same layer, you start to have domains that are

415
00:56:24.210 --> 00:56:32.660
Rm 330: More aligned before you… they're… it's an anti-ferroelectric, but the material is starting to have these bigger and bigger nanodymains.

416
00:56:33.070 --> 00:56:38.199
Rm 330: You can see those energy landscape is actually quite close as you… as you eve down those strains.

417
00:56:39.260 --> 00:56:48.669
Rm 330: That's what we went for. And Sirin, who was Craig's student, became a postdoc with one of Craig's postdocs, Guru.

418
00:56:48.800 --> 00:57:00.220
Rm 330: And calculate it, and you guys know way more about this method, but what the difference would be in terms of the tunneling, in terms of the energetic landscape, as you start to put strain.

419
00:57:00.220 --> 00:57:14.769
Rm 330: So as you start to put strain on the material, it goes from having this very shallow barrier to having this barrier that is higher and further apart, and the result that that has on the positions of the iron is dramatic.

420
00:57:14.770 --> 00:57:26.840
Rm 330: It goes from the irons being, you know, close to the center position as they tunnel back and forth, to being localized on one side, the other. And this is all at strains that we can experimentally assess.

421
00:57:27.760 --> 00:57:37.110
Rm 330: So, same substrate, same idea, commensurate film. Commensurately strained, 1.1% by axial compression.

422
00:57:37.880 --> 00:57:43.009
Rm 330: the punchline. Now, second harmonic Generation starts to show this material's polar.

423
00:57:43.290 --> 00:57:51.729
Rm 330: And the particular point group, the polar point group, changes with temperature, but you can see it's a polar point group by secondary generation.

424
00:57:52.100 --> 00:57:54.239
Rm 330: Now, I want to end with TEM.

425
00:57:54.480 --> 00:58:11.560
Rm 330: And, this is a complicated crystal structure. I was really excited that Craig was willing to do calculations on this thing, but the microscopy is also very, very, complicated. And the contrast that I'll make is between an unstrained single crystal that was grown at Hillbridge in,

426
00:58:13.410 --> 00:58:24.210
Rm 330: somebody's group, David Vandris' group. And so… so what I want to look at, what we want to look at is, is this iron in the string-old bike pyramid off-center?

427
00:58:24.490 --> 00:58:32.570
Rm 330: Well, that iron is this thing right here. This is conventional, this is, you know, state-of-the-art today. Iron glion. That blurry thing.

428
00:58:32.690 --> 00:58:38.089
Rm 330: But with Dave Muller's method, This is what it looks like with multi-slice typography.

429
00:58:38.410 --> 00:58:46.979
Rm 330: you can see that it becomes possible to start to see things, including the blur of this iron. Can you start to see that? It's… okay, it's tough, and then…

430
00:58:47.230 --> 00:58:52.399
Rm 330: Now, so yes, by these methods, it can be seen by Dave Muller's method.

431
00:58:52.960 --> 00:58:53.960
Rm 330: And…

432
00:58:54.220 --> 00:59:01.670
Rm 330: It, Dave Mandris, where the single crystal came from. Now, how's this blur compared to the blur on our… on our, our strained film?

433
00:59:02.390 --> 00:59:11.259
Rm 330: That's what's, shown here, side by side, okay? This line scan. You can see it, maybe down here, you can sort of see it better, okay? This is the unstrained.

434
00:59:11.340 --> 00:59:29.450
Rm 330: This is the strain, okay, down here. Maybe you want to see what the line scans look like. Here's a comparison of the two line scans. Just from this real data. TEAM, room temperature, hopefully you can start to see that these… this is becoming, you know, more bimobile, okay? It's getting further from being off-center.

435
00:59:29.770 --> 00:59:39.090
Rm 330: Now, Dave's technique of typography goes even further. Not only can he calculate It's multi-slice typography.

436
00:59:39.220 --> 00:59:43.220
Rm 330: So not only does he get better resolution, laterally.

437
00:59:43.730 --> 00:59:50.060
Rm 330: Also, he can calculate each slice going through the TEM lamella, so into the board.

438
00:59:50.340 --> 01:00:03.079
Rm 330: So we enter the board, we're going to look every about 2 nanometers, and see where the position of this iron is. And we're going to see, is it… is it all… is it all down? Is it all up? Or what's… what's it doing?

439
01:00:03.640 --> 01:00:05.820
Rm 330: Mr. I'll play the movie.

440
01:00:06.140 --> 01:00:22.759
Rm 330: So we're now looking through the TEM lamella. You asked about this at the beginning. You know, is it… are we seeing a bunch of… a column of atoms on top of each other? Well, with multi-slice typography, Dave is able to look at each slice going through the sample. And I think what you can see is the iron is…

441
01:00:22.760 --> 01:00:37.290
Rm 330: sometimes below the plane, sometimes above the plane. There can be some superposition that you see where your… where the resolution is about 2 to 3 nanometers in the depth of the foil, where there's some superposition of below the plane and above the plane.

442
01:00:37.600 --> 01:00:41.829
Rm 330: These are the polar nanogamates that I'm talking about.

443
01:00:42.460 --> 01:00:53.549
Rm 330: It's in agreement with Craig's calculation. It's also a… A room temperature, relaxer, Altecra.

444
01:00:53.900 --> 01:00:55.730
Rm 330: With that, I'll… I'll end.

445
01:00:57.280 --> 01:00:58.080
Rm 330: Thanks.

446
01:01:03.180 --> 01:01:08.010
Rm 330: Please. Oh, white light's on. White light's on, yeah.

447
01:01:09.860 --> 01:01:14.189
Rm 330: Nice thought. What happened to the magneticism? The base of the Y?

448
01:01:14.360 --> 01:01:15.420
Rm 330: Either case.

449
01:01:16.070 --> 01:01:17.840
Rm 330: In the Barium Hexa Ferry.

450
01:01:17.920 --> 01:01:28.699
Rm 330: And also, even also the first example, the lithium ferrite, is it still magnetic? I have no idea, but we'd love to send you samples. I think you asked the right question.

451
01:01:28.700 --> 01:01:38.340
Rm 330: Yeah, the, I mean, it's hard to… this, this, this, yeah, I mean, that's, that's out of the range of a squid, but… but if you're interested, we'd love to send you samples.

452
01:01:39.150 --> 01:01:58.749
Rm 330: Please. Yeah, and the second part of your talk is the implication that for smaller, strains, you would get a relaxer, but if you really could pump out the strain, you would get a multi-ferroic? That's correct. A room temperature, very magnetic, very electric, but that should take about 5% strain at room temperature. Geological.

453
01:01:59.130 --> 01:02:09.589
Rm 330: Yeah, yeah, I think it's impossible, but yeah. The reason it's a relaxer is because you have the nanopolar domain. That's correct.

454
01:02:10.060 --> 01:02:17.919
Rm 330: Please. Can you go back to the, top view picture at the end of the first part?

455
01:02:18.250 --> 01:02:24.699
Rm 330: Is it a lot of slides, or… Well, just at the end of the first part of the talk, you had a nice, tough room.

456
01:02:25.460 --> 01:02:27.120
Rm 330: Right there.

457
01:02:27.810 --> 01:02:29.429
Rm 330: No way, go forward.

458
01:02:31.980 --> 01:02:34.500
Rm 330: One more. Didn't you add a top field?

459
01:02:34.680 --> 01:02:36.830
Rm 330: No, go back, I guess, I'm sorry.

460
01:02:37.320 --> 01:02:42.659
Rm 330: Is it crystal structure I'm looking for, or… Yeah, the crystal structure… yeah,

461
01:02:44.820 --> 01:02:47.030
Rm 330: So you see the top view on the right over here?

462
01:02:47.750 --> 01:02:58.810
Rm 330: There's a cross-section. Okay, that's the one I want. So, so should I understand, there are… there are two lutetiums and one firon, and all three are at different heights?

463
01:03:00.110 --> 01:03:01.470
Rm 330: And…

464
01:03:01.840 --> 01:03:10.269
Rm 330: But the three-fold symmetry is retained. So this is lutetium, lutetium, lutetium, lutetium. Along this direction, there's two up and one down.

465
01:03:10.500 --> 01:03:13.639
Rm 330: No, no, but you had a picture of the substrate.

466
01:03:15.720 --> 01:03:17.990
Rm 330: Haha, okay.

467
01:03:17.990 --> 01:03:30.220
Rm 330: I know what you're talking about. I think it's coming here. This one? Yeah. Okay, so this one, as I go along, I've got two lutetiums, I've got a high and a low, and then an iron, so all three are at different heights.

468
01:03:30.220 --> 01:03:43.900
Rm 330: This is the bridging there. Yeah, just the bridging, I'm just trying to understand the bridging. Good. So, so, so basically, but it does retain the three-fold symmetry, as seen before. It does, it does. So basically, it's like you're adjusting these three heights.

469
01:03:44.350 --> 01:03:47.090
Rm 330: And I think that, you know, you can argue this is polar.

470
01:03:47.430 --> 01:03:52.690
Rm 330: So, because these… I mean, if these atoms were the same, obviously it would be…

471
01:03:53.050 --> 01:03:59.510
Rm 330: So I'd like to pierces, you know, I think we have bias. The… I think there… I think we are biasing the, the sample in one direction.

472
01:03:59.720 --> 01:04:00.610
Rm 330: Okay.

473
01:04:00.750 --> 01:04:01.870
Rm 330: But you…

474
01:04:02.850 --> 01:04:10.260
Rm 330: Well, you could imagine, if you could tune the heights of these three things, that you could get to a point where actually

475
01:04:11.080 --> 01:04:29.650
Rm 330: you could tune it so that it's actually nonpolar, but still have 3 different heights that would do what you want. Yes. Exactly. We could get some rumpling without having polarization. Yeah. And this was a point where, you know, I asked Craig about, you know, is this thing polar or not? And he…

476
01:04:29.920 --> 01:04:31.909
Rm 330: He did not do a calculation.

477
01:04:31.930 --> 01:04:50.949
Rm 330: But he says he thinks it is polypolar. Yeah, by symmetry you'd expect, but on the other hand, with 3 things to tune, you could tune it, so you could imagine somehow doing chemical substitution or something, you might be able to tune it easily. And then that might be easier to switch. So it might have, you know, the two ground states might be equal.

478
01:04:51.060 --> 01:05:06.029
Rm 330: So, follow up this question. So, Tara, you probably know this, so… so, terra-electric faces, up, up, down, or, down, down, up, but you can have also up, no, downstate.

479
01:05:06.510 --> 01:05:15.750
Rm 330: up, no, no missile, no distortion, and one moves up, the other one moves down. Up, no, down. So that's almost like this one. One of them are rotisser.

480
01:05:15.940 --> 01:05:24.329
Rm 330: So, look, if it's like this… I've seen that in papers, but my microscopy colleagues think that's due to damage.

481
01:05:24.680 --> 01:05:27.659
Rm 330: No, it does happen in India MN03.

482
01:05:27.680 --> 01:05:52.579
Rm 330: Hex7 or indium MN3 has a bulk phase, so-called up, no, downstate, unstable. Okay. It is stable, so it can happen in case form. Okay. And also, if there is all of them are lutetium, then there is actually a no-down state. Okay. Which is getting very similar. So, there may be some connection here. So, you may want to think about this. So, indium, again, indium… hex7 indium MNO3 has this

483
01:05:52.580 --> 01:05:56.690
Rm 330: Lord knows also that up, no, down should be at a domain wall.

484
01:05:56.850 --> 01:06:19.790
Rm 330: We haven't seen it. We haven't seen them actually experimented, have no doubt. Have. It's a domain work of down and down-down. Yeah. The question is this, you're absolutely beautiful anti-PEXA variant, which is a big surprise to me. So, even in bulk sample.

485
01:06:20.200 --> 01:06:25.059
Rm 330: you have this diffusive ion position. Yeah. So I wonder…

486
01:06:25.370 --> 01:06:34.990
Rm 330: Your film is even better, but however, even in single crystal, if you apply electric field, and then you… you do electric field to pull it.

487
01:06:35.070 --> 01:06:51.259
Rm 330: I wonder if you can induce a one-directionalization, and whether it can even switch. So, as you know, federal, and if you do a directional period of cooling, you can make an actual federal election. You can make a real federal election, you know. So, even bulk sample, I wonder if it's going to work.

488
01:06:51.260 --> 01:07:00.060
Rm 330: If the… I think the sample is inflating enough so that you can apply electric field, then you may be able to stabilize one direction. There is a group in China

489
01:07:00.100 --> 01:07:06.689
Rm 330: That has… that claims fair electricity at room temperature in both barium hexaferite and lead hexaferite.

490
01:07:06.990 --> 01:07:14.259
Rm 330: And they show history systems, like you're talking about. Maybe I can show them to you later. They look unusual.

491
01:07:14.560 --> 01:07:16.310
Rm 330: and the…

492
01:07:16.470 --> 01:07:26.349
Rm 330: My worry is that it's due to leakage. Yeah, there's been some collections. So they claim that they have a special oxygen annealing treatment that makes their samples more insulating.

493
01:07:26.410 --> 01:07:44.789
Rm 330: My electrical people have said this looks more like electrochemistry than it does a, actual hysteresis. But I'm happy to show you the data. So the claim is out there. The claim's out there, Sam. Is it a banana, or is it the saturation?

494
01:07:45.230 --> 01:08:08.210
Rm 330: Don't you know about the banana? Yeah, yeah, yeah. It looks better than the banana. The rest of the audience, Jim Scott did a measurement on the banana. He also published a couple of papers, so we…

495
01:08:08.210 --> 01:08:24.770
Rm 330: But he doesn't cite… when he talks about the banana, he cites, like, 20 other papers of other people's work. There's more than, you know.

496
01:08:24.990 --> 01:08:25.670
Rm 330: Sorry.

497
01:08:28.880 --> 01:08:32.859
Rm 330: Great. Well, thank you very much. It's been…

498
01:08:50.990 --> 01:09:15.000
Rm 330: Oh, it's the universe. Okay, thank you.

499
01:09:15.060 --> 01:09:20.319
Rm 330: How strictly is that?