Graphene: Revisiting old questions in a new material

by Shaffique Adam (National Institute of Standards and Technology)

Thursday 9 Feb 2012, 09:00 → 09:50 Europe/Stockholm

122:026

From the hard-drives that harness giant magneto-resistance to the transistors that drive modern processors, solid state physics is at the very heart of the technological revolution. Implied in this effort is a thorough understanding of electronic systems in nanoscale geometries.

In this context, the complex interplay between disorder, electron-electron interactions and quantum interference is an interesting backdrop to many of the unsolved mysteries in condensed matter physics. About five years ago, a new electronic material appeared – notable not only for its ease of preparation and theoretical simplicity, but also by its promise for future electronic devices [1].

Single monatomic sheets of carbon, known as graphene, have an electronic dispersion that is reminiscent of light, in that they can be described as a massless Dirac particle. In many ways, graphene is a textbook system to test physical models – for instance, similar to field-effect transistors, the electron density in graphene sheets can be modulated by a backgate.

However, unlike conventional semiconductors, the carrier density can be continuously tuned from electron-like carriers for large positive gate bias to hole-like carriers for negative bias, with the Dirac point defined as the singularity that marks the transition from electrons to holes. When graphene is close to charge neutrality, its energy landscape becomes highly inhomogeneous, forming a sea of electron-like and hole-like puddles, which determine the properties of graphene at low carrier density.

In this talk, I will discuss how the electronic properties of the Dirac point provide an intriguing example of how the competing effects of disorder, electron-electron interactions, and quantum interference conspire together to give a surprisingly robust state whose properties can be described using semi-classical methods. Armed with this success, I will discuss how future graphene experiments could shed light on some long-standing open questions in condensed matter physics.

References:
[1] S. Das Sarma, S. Adam, E. H. Hwang, E. Rossi, “Electronic transport in two dimensional graphene”, Rev. Mod. Phys. 83, 407 (2011).