Spin polarization enhancement in a single-layer Bi(1-x)Sb(x) alloy on Ag(111) via isovalent substitution

TL;DR

This study demonstrates that substituting Sb for Bi in a single-layer Bi(1-x)Sb(x) alloy on Ag(111) enhances spin polarization due to inversion symmetry breaking, combining experimental and theoretical insights.

Contribution

It provides a concrete example showing how isovalent substitution can significantly increase spin polarization in surface alloys, informing design principles for Rashba systems.

Findings

ARPES and DFT confirm four surface-state bands with spin splitting.

Sb incorporation induces asymmetries leading to sizable spin polarization.

Effects remain significant despite substrate interactions.

Abstract

Co-adsorption of Bi and Sb on Ag(111) at room temperature yields a single-layer Bi(1-x)Sb(x) alloy with a rectangular 3xsqrt(3) structure containing four atoms per unit cell (2/3 ML total coverage) and lacking long-range chemical order. We present an electronic structure study of this system combining angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. To investigate the effect of inversion symmetry breaking induced by substituting a heavier atom (Bi) with a lighter isoelectronic one (Sb) within a fixed crystallographic framework, we focused on a Bi-rich composition. ARPES measurements reveal four surface-state bands, in good agreement with DFT calculations based on a rectangular four-atom overlayer unit cell. DFT calculations further show that Sb incorporation induces both in-plane and out-of-plane asymmetries in the electronic potential, leading to sizable spin splitting and spin polarization of the overlayer bands. Although these effects are partially reduced by interaction with the substrate, they remain significant. Our work illustrates, through a concrete model system, a general principle: incorporating a lighter isovalent element can significantly enhance spin polarization, potentially offering a useful design guideline for understanding and engineering Rashba-related systems.