Envelope-function-based analysis of the dependence of shot noise on the gate voltage in disordered graphene samples

We perform simulations, by means of an envelope-function-based approach, of shot noise in disordered monolayer graphene devices, as a function of the gate bias voltage. In order to approach the experimental conditions, large graphene samples with characteristic sizes of the order of hundreds of nanometers or microns have been considered. We investigate different device geometries, including back-gated graphene samples with different aspect ratios and a graphene constriction biased by two side gates. We compare our results with available experimental data that were collected by a few authors in an attempt to validate an interesting prediction made by Tworzydło et al. [Phys. Rev. Lett. 96, 246802 (2006)] on the shot noise dependence on carrier density in samples with a large aspect ratio. On the basis of the comparison of our results with the experimental data, we conclude that the effect predicted by Tworzydło et al. (resulting from the distribution of the transmission eigenvalues associated with propagation via evanescent modes) has not been observed yet. Finally, we provide some guidelines for the design of experiments aimed at the verification of such an effect.