Conductance quantization in graphene nanoconstrictions with mesoscopically smooth but atomically stepped boundaries

TL;DR

This study uses large-scale quantum transport calculations to show that graphene nanoconstrictions with mesoscopically smooth but atomically stepped edges exhibit conductance quantization, including a plateau near half the quantum unit, even without electron interactions.

Contribution

It demonstrates that conductance quantization and the 0.5*2e2/h plateau can occur due to edge steps and non-adiabatic scattering without electron-electron interactions.

Findings

Conductance quantized in integer multiples of 2e2/h.

Presence of a conductance plateau near 0.5*2e2/h.

Quantization occurs despite non-adiabatic backscattering.

Abstract

We present the results of million atom electronic quantum transport calculations for graphene nanoconstrictions with edges that are smooth apart from atomic scale steps. We find conductances quantized in integer multiples of 2e2/h and a plateau at ~0.5*2e2/h as in recent experiments [Tombros et al., Nature Physics 7, 697 (2011)]. We demonstrate that, surprisingly, conductances quantized in integer multiples of 2e2/h occur even for strongly non-adiabatic electron backscattering at the stepped edges that lowers the conductance by one or more conductance quanta below the adiabatic value. We also show that conductance plateaus near 0.5*2e2/h can occur as a result of electron backscattering at stepped edges even in the absence of electron-electron interactions.