Spin-charge coupled transport in van der Waals systems with random tunneling

M Rodriguez-Vega,G Schwiete,Enrico Rossi

doi:10.1103/physrevresearch.1.033085

Abstract

We study the electron and spin transport in a van der Waals system formed by one layer with strong spin-orbit coupling and a second layer without spin-orbit coupling, in the regime when the interlayer tunneling is random. We find that in the layer without intrinsic spin-orbit coupling spin-charge coupled transport can be induced by two distinct mechanisms. First, the gapless diffusion modes of the two isolated layers hybridize in the presence of tunneling, which constitutes a source of spin-charge coupled transport in the second layer. Second, the random tunneling introduces spin-orbit coupling in the effective disorder-averaged single-particle Hamiltonian of the second layer. This results in non-trivial spin transport and, for sufficiently strong tunneling, in spin-charge coupling. As an example, we consider a van der Waals system formed by a two-dimensional electron gas (2DEG)--such as graphene--and the surface of a topological insulator (TI) and show that the proximity of the TI induces a coupling of the spin and charge transport in the 2DEG. In addition, we show that such coupling can be tuned by varying the doping of the TI's surface. We then obtain, for a simple geometry, the current-induced non-equilibrium spin accumulation (Edelstein effect) caused in the 2DEG by the coupling of charge and spin transport.

Highlights

In recent years experimentalists have been able to make very novel and high-quality heterostructures that allow the realization of new effects and states of great fundamental and technological interest [1]
In this work we focus on this situation and study the electron and spin transport in a two-dimensional van der Waals system comprised of one component with strong spin-orbit coupling (SOC) and one with no, or negligible, SOC, when the interlayer tunneling is random
We have studied the electron and spin transport in a van der Waals system formed by one layer with strong spin-orbit coupling and a second layer without spinorbit coupling, in the regime when the interlayer tunneling is random

Summary

INTRODUCTION

In recent years experimentalists have been able to make very novel and high-quality heterostructures that allow the realization of new effects and states of great fundamental and technological interest [1]. We find that in general, if the diffusive transport in the layer with SOC exhibits spin-charge coupling [26,27,28] such coupling will be present in the layer without SOC, i.e., in the most common experimental situation To exemplify this general result we consider the case of a van der Waals system formed by a two-dimensional electron gas (2DEG) placed on the surface of a strong three-dimensional topological insulator (TI) [29,30,31]. Such as Bi2Se3 have almost commensurate lattices and as a consequence in many graphene-TI heterostructures the K, K points of the graphene’s Brillouin zone are folded close to the TI’s point [19] This fact, combined with the random and finite-range nature of the interlayer tunneling, implies that the results that we obtain for a 2DEG-TI van der Waals system are directly relevant to graphene-TI heterostructures.

MICROSCOPIC APPROACH

DIFFUSION EQUATIONS

APPLICATIONS

CONCLUSIONS