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

TL;DR

This study investigates high-bias electronic conductivity and shot noise in bilayer graphene, revealing electron-optical phonon interactions and their impact on transport properties at elevated electronic temperatures.

Contribution

It provides the first detailed analysis of shot noise and conductivity saturation in bilayer graphene at high bias, linking electron-phonon coupling to transport behavior.

Findings

Conductivity initially increases then saturates and decreases due to optical phonon backscattering.

Shot noise decay indicates electron-phonon interactions at high bias.

Electron temperature reaches ~1200 K at 0.75 V bias.

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 $\sim1200$ 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.