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

TL;DR

This paper develops a nonequilibrium Green function theory to analyze quantum coherence and dephasing effects in the giant spin Hall effect and nonlocal voltages in multiterminal graphene, explaining experimental observations across various conditions.

Contribution

It introduces a NEGF-based model incorporating dephasing to explain spin Hall and nonlocal voltage phenomena in graphene Hall bars, aligning theory with experiments.

Findings

Large spin Hall conductance at the Dirac point in phase-coherent regime

Dephasing significantly reduces spin Hall and nonlocal voltages

Features are washed out away from the Dirac point due to dephasing

Abstract

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