Charge, spin and pseudospin in graphene

Graphene, a one-atom-thick form of carbon, has emerged in the last few years as a fertile electron system, highly promising for both fundamental research and applications. In this thesis we consider several topics in electronic and spin properties of graphene, with a particular emphasis on the quantum Hall effect (QHE) regime, where this material exhibits most interesting behavior. We shall start with analyzing general properties of the two-terminal conductance for graphene mono- and bilayer samples. Using conformal invariance and the theory of conformal mappings, we characterize the dependence of conductance on the sample shape. We identify the features which distinguish monolayers and bilayers and illustrate the use of the two-terminal conductance as a tool for sample diagnostic. Next, we present a microscopic study of the edge states in the QHE regime. This analysis provides a simple and general explanation of the half-integer Hall quantization in graphene. We discuss the edge states dispersion for different orientations of the boundary, and propose a way to image the edge states using STM spectroscopy. Then, we extend the picture of edge states to describe QHE in spatially nonuniform systems, recently demonstrated p-n and p-n-p devices. We show that the bipolar p-n and p-n-p junctions can host counter-circulating QHE edge states, which mix at the p-n interfaces, giving rise to fractional and integer quantization of the two-terminal conductance, observed in this structures. Graphene exhibits interesting spin- and valley-polarized QH ferromagnetic (FM) states. We show that spin-polarized QH state at zero doping hosts counter-circulating edge states carrying opposite spins, and propose to use this regime as a vehicle to study spin transport. We study ordering in the valley-polarized QH state.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Abanin, Dmitry A

Advisor dc:contributor.advisor

• Leonid S. Levitov.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/45449

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/45449