Even Zero Dimensions Ain't Easy - The Wonderful World of Quantum Dots

Chris Hooley

Abstract

The aim of this session is to give some basic feeling for the physics of so-called "quantum dots". These devices consist of a small (essentially zero-dimensional) cluster of confined electrons (the dot), connected to two or more leads, across which a potential difference may be applied. Strong correlations between the electrons on the dot can play an important role in the physics - hence they are sometimes called "artificial atoms".

(The technological possibilities are allegedly impressive. Words like "nanotronics" are bursting out all over the shop these days.)

This field is quite new, but don't assume that an overview is therefore easy or short! The rough plan is as follows:

• How are they made? (semiconductors, nanotubes, self-assembly, etc.)
• What is the basic physics of a single dot connected to two leads? (Coulomb blockade, closed/open dots)
• How does the spin of the dot electrons affect the basic picture? (odd-even effects, the Kondo effect) This part will include a review of the Kondo effect in general, so don't worry if you don't know what it is.

• What happens when the voltage across the dot is large?

References:

THE KONDO EFFECT

J. Kondo, Prog. Theor. Phys. 32, 37 (1964).

	Kondo points out that you can explain the resistance
	minimum in dilute alloys using the idea of spin-flip
	interactions with impurities.

Hewson, A. C.
"The Kondo Effect to Heavy Fermions"

	A good book about Kondo physics.  Technically a bit heavy,
	but if you want more than the standard "spin gets screened"
	hand-waving, a fine place to start.

P. W. Anderson, J. Phys. C 3, 2436 (1970).

	A nice paper talking about a simple version of
	renormalisation for the Kondo problem.


QUANTUM DOTS

I. Aleiner et al, "Quantum Effects in Coulomb Blockade", cond-mat/0103008

	Probably the best (and most up-to-date) available review
	of the physics of closed quantum dots.  Most of the original
	papers are referenced in this article.

Goldhaber-Gordon et al., cond-mat/9707311
Cronenwett et al., cond-mat/9804211
W.G. van der Wiel et al., Science 289, 2105 (2000)

(the first two have been published - I just don't have the references to
hand)

	Experimental observation of the Kondo effect in
	quantum dots.  Follow references in these papers
	for more background on Coulomb blockade and so forth.
	The data in the third paper (van der Wiel et al.)
	are marvellous: you can really see the conductance
	reach the quantum limit all the way across the
	Coulomb valley.