▎ 摘　　要

Ideal Sharvin contact in a multimode regime shows the conductance G approximate to G(Sharvin) = g(0)k(F)W/pi (with g(0) the conductance quantum, k(F) the Fermi momentum, and W the contact width) accompanied by strongly suppressed shot noise quantified by small Fano factor F approximate to 0. For ballistic graphene away from the charge-neutrality point, sub-Sharvin transport occurs, characterized by suppressed conductance G approximate to (pi/4) GSharvin and enhanced shot noise F approximate to 1/8. All these results can be derived from a basic model of quantum scattering, involving assumptions of infinite height and a perfectly rectangular shape of the potential barrier in the sample. Here we have carried out the numerical analysis of the scattering on a family of smooth barriers of finite height interpolating between parabolic and rectangular shapes. We find that, tuning the barrier shape, one can modify the asymmetry between electron- and hole-doped systems. For electronic dopings, the system crosses from the Sharvin to sub-Sharvin transport regime (indicated by both the conductance and the Fano factor) as the potential becomes closer to the rectangular shape. In contrast, for hole dopings, the conductivity is strongly suppressed when the barrier is parabolic and slowly converges to G approximate to (pi/4) GSharvin as the potential evolves toward a rectangular shape. In such a case, the Sharvin transport regime is inaccessible, shot noise is generically enhanced (with much slower convergence to F approximate to 1/8) compared to the electron-doped case, and aperiodic oscillations of both G and F are prominent due to the formation of quasibound states.