Conductivity and shot noise in graphene contain both interesting information on the nature of transport of charge carriers. For ballistic mono-layer graphene, the conductivity and the excess noise Fano factor are 4e²/πh and 1/3 at the charge neutrality point, respectively [1,2]. At high bias voltage, the electron-electron and electron-phonon interactions should lead to a breakdown of ballistic transport and, therefore, modify conductivity and shot noise.
We have studied electrical conductivity σ and shot noise of bilayer graphene sheets at high bias voltage Vds [3]. As a function of bias, we find a linear increase of σ which is leveled off above Vds~0.2 V. In the linear region, a simple scaling law is found between the bias and gate voltage dependences of σ. The Fano factor F is found to first increase with bias and then reach a maximum at Vds~0.1 V, above which F decreases.
A mean-free-path type model is used to analyze the results. The increase of σ is directly related to the increase of the transmission modes within the bias widows [4]. We assign the saturation of σ and the decrease of F to the creation of optical/zone boundary phonons. F is also used as a thermometer to measure the electronic temperature. This defined temperature is in good agreement with that extracted from the conductivity model.

Refs. :
[1] R. Danneau, F. Wu, M.F. Craciun, S. Russo, M.Y. Tomi, J. Salmilehto, A.F. Morpurgo, and P.J. Hakonen, Phys. Rev. Lett. 100, 196802 (2008); J. Low. Temp. Phys. 153, 374 (2008); Solid State Commum. (in press)
[2] J. Tworzydlo, B. Trauzettel, M. Titov, A. Rycerz, and C.W.J. Beenakker, Phys. Rev. Lett. 96, 246802 (2006)
[3] A. Fay, J.K. Viljas, R. Danneau, F. Wu, M.Y. Tomi, J. Wengler, M. Wiesner, and P.J. Hakonen, arXiv:0904.4446v1
[4] E.B. Sonin, Phys. Rev. B 77, 233408 (2008)