Strongly spin-orbit coupled two-dimensional electron gas emerging near the surface of polar semiconductors

TL;DR

This study reveals giant Rashba-type spin-splitting in 2D electron layers near the surface of polar semiconductors BiTeX, driven by strong spin-orbit interaction and polarity, with effects observable in both conduction and valence bands.

Contribution

It provides direct experimental evidence of large Rashba spin-splitting in 2D electron gases on polar semiconductor surfaces, linking Rashba strength to band-gap size.

Findings

Giant Rashba spin-splitting observed in conduction-band subbands.

Spin-split subbands show X-dependent Rashba coupling.

Valence bands also exhibit 2D confinement effects.

Abstract

We investigate the two-dimensional (2D) highly spin-polarized electron accumulation layers commonly appearing near the surface of n-type polar semiconductors BiTeX (X = I, Br, and Cl) by angular-resolved photoemission spectroscopy. Due to the polarity and the strong spin-orbit interaction built in the bulk atomic configurations, the quantized conduction-band subbands show giant Rashba-type spin-splitting. The characteristic 2D confinement effect is clearly observed also in the valence-bands down to the binding energy of 4 eV. The X-dependent Rashba spin-orbit coupling is directly estimated from the observed spin-split subbands, which roughly scales with the inverse of the band-gap size in BiTeX.