Quantum coherence and its dephasing in the giant spin Hall effect and nonlocal voltage generated by magnetotransport through multiterminal graphene bars

摘要

Motivated by the recent experimental observation [D. A. Abanin et al.,Science 323, 328 (2011)] of nonlocality in magnetotransport near the Diracpoint in six-terminal graphene Hall bars, for a wide range of temperatures andmagnetic fields, we develop a nonequilibrium Green function (NEGF) theory ofthis phenomenon. In the phase-coherent regime and strong magnetic field, wefind large spin Hall (SH) conductance in four-terminal bridges, where the SHcurrent is pure only at the Dirac point (DP), as well as the nonlocal voltageat a remote location in six-terminal bars where the direct and inverse SHeffect operate at the same time. The "momentum-relaxing" dephasing reducestheir values at the DP by two orders of magnitude while concurrently washingout any features away from the DP. Our theory is based on the Meir-Wingreenformula with dephasing introduced via phenomenological many-body self-energies,which is then linearized for multiterminal geometries to extract currents andvoltages.