Pseudodiffusive magnetotransport in graphene

Transport properties through wide and short ballistic graphene junctions are studied in the presence of arbitrary dopings and magnetic fields. No dependence on the magnetic field is observed at the Dirac point for any current cumulant, just as in a classical diffusive system, both in normal-graphene-normal and normal-graphene-superconductor junctions. This pseudodiffusive regime is, however, extremely fragile with respect to doping at finite fields. We identify the crossovers to a field-suppressed and a normal ballistic transport regime in the magnetic-field-doping parameter space, and provide a physical interpretation of the phase diagram. Remarkably, pseudodiffusive transport is recovered away from the Dirac point in resonance with Landau levels at high magnetic fields.

Figure 1

(Color online) (a) Inverse longitudinal resistivity in units of $4e^2∕\pi h$ and (b) bulk Fano factor for the N (left) and NS (right) junctions as a function of the (absolute value of the) Fermi energy (in units of $\hslash v_F∕L$). Different curves correspond to different values of $L∕l_B$ (where $l_B\equiv \sqrt{\hslash ∕eB}$), which ranges from zero for red curve to 4 for the dark blue one in steps of 1. The same for the ratio $G_{\mathrm{NS}}^{\text{bulk}}∕G_{\mathrm{N}}^{\text{bulk}}$ in the inset.

Figure 2

(Color online) Phase diagram representing the crossovers from localized, pseudodiffusive, and ballistic transport regimes in the field-doping parameter plane. The solid (dashed) lines represent the boundaries for a N (NS) junction. LLs are labeled by $n$.