Surface Circular Photogalvanic Effect in Tl-Pb Monolayer Alloys on Si(111) with Giant Rashba Splitting

Abstract

We have found that surface superstructures made of "monolayer alloys" of Tl and Pb on Si(111), having giant Rashba effect, produce non-reciprocal spin-polarized photocurrent via circular photogalvanic effect (CPGE) by obliquely shining circularly polarized near-infrared (IR) light. CPGE is here caused by injection of in-plane spin into spin-split surface-state bands, which is observed only on Tl-Pb alloy layers, but not on single-element Tl nor Pb layers. In the Tl-Pb monolayer alloys, despite their monatomic thickness, the magnitude of CPGE is comparable to or even larger than the cases of many other spin-split thin-film materials. The data analysis has provided the relative permittivity ${\epsilon }^{\ast }$ of the monolayer alloys to be $\sim$ 1.0, which is because the monolayer exists at a transition region between the vacuum and the substrate. The present result opens the possibility that we can optically manipulate spins of electrons even on monolayer materials.

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