SEMINAR on Disorder and Strong Correlations: "Topological quantum criticality of Dirac fermions: From graphene to topological insulators"

[statphys]

CONDENSED MATTER AND
STATISTICAL PHYSICS SECTION

SEMINAR  on  Disorder and Strong Correlations

Thursday, 5 November    -    11:00 a.m.

Seminar Room
ICTP Leonardo Building - 1st floor

A. MIRLIN
(Karlsruhe Institute of Technology)

"Topological quantum criticality of Dirac fermions:
 From graphene to topological insulators"

Abstract
Critical phenomena and quantum phase transitions are paradigmatic 
concepts in modern condensed matter physics. A central example in the 
field of mesoscopic physics is the localization-delocalization 
(metal-insulator) quantum phase transition driven by disorder -- the 
Anderson transition. Although the notion of localization has appeared 
half a century ago, this field is still full of surprising new 
developments.  In this talk, I will discuss novel materials---graphene 
and topological insulators---where the charge carriers have a character 
of 2D Dirac fermions. A non-trivial topological nature of the 
corresponding theories leads to remarkable physical consequences. In 
graphene, the charge carriers turn out to be topologically protected 
from Anderson localization, as long as the intervalley scattering can be 
neglected. A similar phenomenon takes place for surface modes of a 3D 
topological insulator. Furthermore, we show that, in the latter system, 
the Coulomb interaction leads to emergence of a quantum critical state. 
Remarkably, the interaction-induced critical state emerges on the 
surface of a three-dimensional topological insulator without any 
adjustable parameters. This ``self-organized quantum criticality'' is a 
novel concept in the field of interacting disordered systems. Finally, 
we predict a quantum spin-Hall transition between the normal and 
topological insulator phases in 2D that occurs via a similar (or 
identical) quantum critical point.