Shot noise and conductivity at high bias in bilayer graphene: Signatures of electron-optical phonon coupling

Abstract

We have studied electronic conductivity and shot noise of bilayer graphene (BLG) sheets at high bias voltages and low bath temperature $T_0=4.2$ K. As a function of bias, we find initially an increase of the differential conductivity, which we attribute to self-heating. At higher bias, the conductivity saturates and even decreases due to backscattering from optical phonons. The electron-phonon interactions are also responsible for the decay of the Fano factor at bias voltages $V>0.1$ V. The high bias electronic temperature has been calculated from shot noise measurements, and it goes up to $\sim 1200$ K at $V=0.75$ V. Using the theoretical temperature dependence of BLG conductivity, we extract an effective electron-optical phonon scattering time ${\tau }_{e-op}$. In a 230 nm long BLG sample of mobility $\mu =3600$ cm${}^2$V${}^{-1}$s${}^{-1}$, we find that ${\tau }_{e-op}$ decreases with increasing voltage and is close to the charged impurity scattering time ${\tau }_{imp}=60$ fs at $V=0.6$ V.

7 pages, 7 figures. Extended version of the high bias part of version 1. The low bias part is discussed in arXiv:1102.0658