Interface enhanced helicity dependent photocurrent in metal/semimetal bilayers

TL;DR

This study investigates how metal/semimetal bilayers enhance helicity dependent photocurrent (HDP), revealing interface effects and sign reversal phenomena, with implications for spintronic device interfaces.

Contribution

It demonstrates that metal/Bi bilayers significantly enhance HDP compared to Bi alone and elucidates the interfacial mechanisms causing sign reversal under back illumination.

Findings

HDP is enhanced in metal/Bi bilayers compared to Bi alone.

Sign of HDP reverses under back illumination in bilayers.

Interfacial spin absorption and conversion cause sign reversal.

Abstract

One of the hallmarks of light-spin interaction in solids is the appearance of photocurrent that depends on the light helicity. Recent studies have shown that helicity dependent photocurrent (HDP) emerges due to light induced spin current and the inverse spin Hall effect of semimetal thin films. We have studied HDP in metal/semimetal bilayers. Compared to Bi single layer films, we find the HDP is enhanced in metal/Bi bilayers. For the bilayers, the sign of HDP under back illumination reverses from that of front illumination. The back illumination photocurrent is the largest for Ag/Bi bilayers among the bilayers studied. Using a diffusive spin transport model, we show that the HDP sign reversal under back illumination is caused by spin absorption and spin to charge conversion at the interface. Such interfacial effects contribute to the HDP enhancement under front illumination for the bilayers when the Bi layer thickness is small. These results show that the HDP can be used to assess interface states with strong spin orbit coupling.