Evanescent wave transport and shot noise in graphene: ballistic regime and effect of disorder

TL;DR

This study explores how evanescent wave transport and shot noise behave in graphene devices, highlighting the effects of disorder and lead alignment on electrical properties in the ballistic regime.

Contribution

It provides experimental measurements of shot noise and conductivity in graphene, confirming theoretical predictions and analyzing the impact of disorder and lead geometry.

Findings

Minimum conductivity of 4e^2/πh observed

Fano factor reaches 1/3 at the Dirac point

Disorder and lead alignment influence transport properties

Abstract

We have investigated electrical transport and shot noise in graphene field effect devices. In large width over length ratio $W/L$ graphene strips, we have measured shot noise at low frequency ($f$ = 600--850 MHz) in the temperature range of 4.2--30 K. We observe a minimum conductivity of $\frac{4e^{2}}{\pi h}$ and a finite and gate dependent Fano factor reaching the universal value of 1/3 at the Dirac point, i.e. where the density of states vanishes. These findings are in good agreement with the theory describing that transport at the Dirac point should occur via evanescent waves in perfect graphene samples with large $W/L$. Moreover, we show and discuss how disorder and non-parallel leads affect both conductivity and shot noise.