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

Fay, A.
Danneau, R.
Viljas, J. K.
Wu, F.
Tomi, M. Y.
Wengler, J.
Wiesner, M.
Hakonen, P. J.
Description
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.
Comment: 7 pages, 7 figures. Extended version of the high bias part of version 1. The low bias part is discussed in arXiv:1102.0658
Keywords
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science