For distribution

[CM ICTP - Trieste]

SEMINAR on   Disorder and strong electron correlations


Monday, 2 April   -    11:00 a.m.



Lecture Room 'C',  Main Bldg.- terrace level


V. FAL'KO    ( Lancaster University )

"Caustics, focusing and Veselago lens in P-N junctions in graphene"

Abstract

	There are many similarities between optics and electronics: Rays in 
geometrical optics are analogous to classical trajectories of 
electrons, while electron de Broglie waves can interfere.  The electron 
microscope is one example of the technological implementation of this 
similarity.  The analogy with optics may also hold a significant 
potential for semiconductor electronics.  In optics, transparent 
interfaces between materials are used in lenses and prisms to 
manipulate light beams.  From this perspective, an unusual promise is 
offered by the recently discovered two-dimensional gapless 
semiconductor, graphene.  Fine-tuning of the carrier density in 
graphene by means of electrical gates or doping of the underlying 
substrate was demonstrated, thus, paving the way towards controllable 
ballistic PNJs.  On the one hand, the PNJ in graphene is highly 
transparent for the charge carriers.  On the other, the transmission of 
electrons through the p-n interface may resemble optical refraction at 
the surface of metamaterials with negative refractive index: the 
straight interface is able to focus electric current whereas a 
ballistic stripe of p-type graphene separating two n-type regions acts 
as a lens.  In this talk, I shall review the properties of graphene and 
p-n junctions in this material leading to the focusing effect, discuss 
form of cautics replacing the focus in asymmetric p-n junctions, and 
describe the proposal of Veselago lens and focusing prism/beam splitter 
in graphene.

References:

V. Cheianov, V.I. Fal’ko, B.L. Altshuler - Science 315, 1252 (2007)
V. Cheianov and V.I. Fal’ko - Phys. Rev. B 74, 041403 (2006)