Competing Disorder and Coulomb Interaction Effects in Graphene

Speaker:

Matthew Foster, Columbia University

Date & Time:

June 16, 2008 - 4:45pm

Location:

Serin E385

Competing Disorder and Coulomb Interaction Effects in Graphene Physics and Astronomy
Matthew Foster, Columbia University Special Condensed Matter Seminar Monday, 4:45 PM Serin E385 Abstract: The recent experimental realization of graphene, a single atomic monolayer of graphite, has refocused attention upon many fundamental questions regarding electronic transport in low dimensions. The observation of an apparent "minimum metallic conductivity" of order e2/h, persistent to the lowest temperatures yet measured in substrate-supported films, has challenged convention notions of electron localization in low dimensions. One expects that the effects of quenched disorder play a crucial role in limiting the low-temperature transport; on the other hand, one cannot neglect the simultaneous effects of electron-electron interactions, which are quite "strong" in this material, especially near the Dirac point. In this work, we analyze the competing effects of Coulomb electron-electron interactions and weak quenched disorder in graphene. Within a large-N generalization employed to treat moderate to strong interactions, we analyze the low-temperature renormalization effects due to both disorder and interactions. We identify two asymptotic transport regimes, which we refer to as "disorder-limited" and "interaction-limited." In the former case, we translate our results into scaling predictions for thermoelectric transport, with a view toward suspended graphene devices. In the "interaction-limited" regime, we demonstrate that (a) a minimum metallic conductivity can arise due entirely to real, inelastic electron-hole collisions (at the Dirac point), and (b) violations of the Mott formula for thermopower are expected at high temperatures, in the degenerate (doped) regime. The latter have been recently observed by Y. Zuev and P. Kim in substrate-supported devices. Ref: Phys. Rev. B 77 195413 (2008).

Competing Disorder and Coulomb Interaction Effects in Graphene
Physics and Astronomy

Matthew Foster, Columbia University
Special Condensed Matter Seminar
Monday, 4:45 PM Serin E385

Abstract: The recent experimental realization of graphene, a single atomic monolayer of graphite, has refocused attention upon many fundamental questions regarding electronic transport in low dimensions. The observation of an apparent "minimum metallic conductivity" of order e2/h, persistent to the lowest temperatures yet measured in substrate-supported films, has challenged convention notions of electron localization in low dimensions. One expects that the effects of quenched disorder play a crucial role in limiting the low-temperature transport; on the other hand, one cannot neglect the simultaneous effects of electron-electron interactions, which are quite "strong" in this material, especially near the Dirac point.

In this work, we analyze the competing effects of Coulomb electron-electron interactions and weak quenched disorder in graphene. Within a large-N generalization employed to treat moderate to strong interactions, we analyze the low-temperature renormalization effects due to both disorder and interactions. We identify two asymptotic transport regimes, which we refer to as "disorder-limited" and "interaction-limited." In the former case, we translate our results into scaling predictions for thermoelectric transport, with a view toward suspended graphene devices. In the "interaction-limited" regime, we demonstrate that (a) a minimum metallic conductivity can arise due entirely to real, inelastic electron-hole collisions (at the Dirac point), and (b) violations of the Mott formula for thermopower are expected at high temperatures, in the degenerate (doped) regime. The latter have been recently observed by Y. Zuev and P. Kim in substrate-supported devices.
Ref: Phys. Rev. B 77 195413 (2008).

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Competing Disorder and Coulomb Interaction Effects in Graphene