Evanescent Wave Transport and Shot Noise in Graphene: Ballistic Regime and Effect of Disorder

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 4e2πh and a finite and gate dependent Fano factor reaching the universal value of 13 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

Transport in graphene nanostructures

“…The experimentally observed conductivity minima σ min depend on sample geometry, disorder (i.e., doping fluctuations and electron-hole puddles), and overall doping of the graphene flake [3,51]. Several experiments [3,51,57,58] on samples with similar geometries show such a minimum conductance value. The presence of the conductivity minimum σ min has major impact on the electrostatic tunability of graphene devices [42], making it difficult to fully pinch off currents in 2-D graphene devices.…”

Impact of Vacancies on Diffusive and Pseudodiffusive Electronic Transport in Graphene

“…For large W/L ratios and energies E around the Dirac point, the system exhibits a pseudodiffusive transport regime [15,[31][32][33][34][35][36], where the conductive channels of the contacts tunnel through the undoped region a with constant minimum conductivity…”

Coupling between electrons and optical phonons in suspended bilayer graphene

“…Our experiments were performed on a pulsetube-based dilution refrigerator operated around 0.5 K. For experimental details, we refer to Refs. [41,42].…”