Pure spin photocurrents in low-dimensional structures

TL;DR

This paper reveals that unpolarized light absorption in semiconductor quantum wells can generate pure spin currents without net charge or spin polarization, expanding understanding of spin photonics.

Contribution

It introduces the novel concept that unpolarized light can produce pure spin currents in low-dimensional semiconductor structures, a phenomenon not previously recognized.

Findings

Pure spin currents can be generated by unpolarized light in quantum wells.

This occurs across various optical transitions including interband, intersubband, and intraband.

Both average electron spin and electric current remain zero during this process.

Abstract

As is well known the absorption of circularly polarized light in semiconductors results in optical orientation of electron spins and helicity-dependent electric photocurrent, and the absorption of linearly polarized light is accompanied by optical alignment of electron momenta. Here we show that the absorption of unpolarized light leads to generation of a pure spin current, although both the average electron spin and electric current vanish. We demonstrate this for direct interband and intersubband as well as indirect intraband (Drude-like) optical transitions in semiconductor quantum wells (QWs).