Zero-bias spin separation

TL;DR

This paper demonstrates a novel form of spin separation induced by spin-dependent scattering of electrons, observable through terahertz radiation absorption, and does not require an electrical bias, differing from the spin Hall effect.

Contribution

It introduces a new mechanism for spin separation driven by spin-dependent scattering without electrical current, expanding understanding of spin manipulation in semiconductors.

Findings

Spin separation achieved without electric current.

Observation of spin separation via terahertz absorption across wide temperature range.

Electron heating alone can induce spin separation through energy relaxation processes.

Abstract

Spin-orbit coupling provides a versatile tool to generate and to manipulate the spin degree of freedom in low-dimensional semiconductor structures. The spin Hall effect, where an electrical current drives a transverse spin current and causes a nonequilibrium spin accumulation observed near the sample boundary, the spin-galvanic effect, where a nonequilibrium spin polarization drives an electric current, or the reverse process, in which an electrical current generates a nonequilibrium spin polarization, are all consequences of spin-orbit coupling. In order to observe a spin Hall effect a bias driven current is an essential prerequisite. The spin separation is caused via spin-orbit coupling either by Mott scattering (extrinsic spin Hall effect) or by Rashba or Dresselhaus spin splitting of the band structure (intrinsic spin Hall effect). Here we provide evidence for an elementary effect causing spin separation which is fundamentally different from that of the spin Hall effect. In contrast to the spin Hall effect it does not require an electric current to flow: It is spin separation achieved by spin-dependent scattering of electrons in media with suitable symmetry. We show that by free carrier (Drude) absorption of terahertz radiation spin separation is achieved in a wide range of temperatures from liquid helium up to room temperature. Moreover the experimental results give evidence that simple electron gas heating by any means is already sufficient to yield spin separation due to spin-dependent energy relaxation processes of nonequilibrium carriers.