Electric field induced metallization of correlated
electron oxides
Stuart S.P. Parkin
The
electric field induced metallization of insulating oxides is a powerful means
of exploring and creating novel electronic states. Recently large internal electric fields from
polar surfaces have been used to create emergent metallic, superconducting and
magnetic states at interfaces between two insulating oxides.
However, the origin of the metallicity is a subject of considerable debate,
especially as to whether charged carriers are induced electrostatically. We show that by placing various oxide
surfaces and thin films in contact with charged fluids these nominally
insulating materials can be transformed into metallic conductors and that the
mechanism is rather due to the flow of ionic currents of oxygen to and fro
between the oxide surface and the liquid1-3. We
discuss, in particular, the electrolyte gating of epitaxial films of vanadium dioxide
(VO2). VO2
exhibits a transition from an insulating to a metallic state above a
metal-insulator transition temperature, TMIT, that depends on strain
induced in the film by epitaxy with underlayers and/or the substrate material
and crystal orientation4. Using in-situ
gating we use x-ray diffraction to show that the out-of-plane lattice constant
can be reversibly changed by more than 3.5% using ionic liquid gating. The possibility of novel, highly energy
efficient “liquid” electronics is discussed.
1 Jeong, J. et al. Suppression of Metal-Insulator
Transition in VO2 by Electric Field–Induced Oxygen Vacancy
Formation. Science 339, 1402-1405, (2013).
2 Li, M. et al.
Suppression of Ionic Liquid Gate-Induced Metallization of SrTiO3(001)
by Oxygen. Nano Lett. 13, 4675-4678 (2013).
3 Schladt, T. D. et
al. Crystal-facet dependent metallization in electrolyte-gated rutile TiO2
single crystals. ACS Nano 7, 8074–8081 (2013).
4 Aetukuri, N. B.
et al. Control of the metal-insulator transition in vanadium dioxide by
modifying orbital occupancy. Nat. Phys.
9, 661-666, (2013).
Host: Prof. V. Podzorov