Quantum transport at the Dirac point: Mapping out the minimum conductivity from pristine to disordered graphene
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PhysRevB.92.205408.pdf
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Author(s)
Tseng, Frank
Habib, K. M. Masum
Ghosh, Avik W.
Sajjad, Redwan Noor
Date Issued
November 2015
Journal
Physical Review B
Publisher
American Physical Society
Citation
Sajjad, Redwan N., Frank Tseng, K. M. Masum Habib, and Avik W. Ghosh. “Quantum Transport at the Dirac Point: Mapping Out the Minimum Conductivity from Pristine to Disordered Graphene.” Physical Review B 92, no. 20 (November 2015). © 2015 American Physical Society
Version
Final published version
Abstract
The phase space for graphene's minimum conductivity σ[subscript min] is mapped out using Landauer theory modified for scattering using Fermi's golden rule, as well as the nonequilibrium Green's function (NEGF) simulation with a random distribution of impurity centers. The resulting “fan diagram” spans the range from ballistic to diffusive over varying aspect ratios (W/L), and bears several surprises. The device aspect ratio determines how much tunneling (between contacts) is allowed and becomes the dominant factor for the evolution of σ[subscript min] from ballistic to diffusive regime. We find an increasing (for W/L > 1) or decreasing (W/L < 1) trend in σ[subscript min] vs impurity density, all converging around 128q[superscript 2]/π[superscript 3]h ~ 4q[superscript 2]/h at the dirty limit. In the diffusive limit, the conductivity quasisaturates due to the precise cancellation between the increase in conducting modes from charge puddles vs the reduction in average transmission from scattering at the Dirac point. In the clean ballistic limit, the calculated conductivity of the lowest mode shows a surprising absence of Fabry-Pérot oscillations, unlike other materials including bilayer graphene. We argue that the lack of oscillations even at low temperature is a signature of Klein tunneling.
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
Massachusetts Institute of Technology. Microsystems Technology Laboratories
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DOI of Published Version
https://doi.org/10.1103/PhysRevB.92.205408
