Alkali-metal induced band structure deformation investigated by angle-resolved photoemission spectroscopy and first-principles calculations

TL;DR

This study combines ARPES experiments and first-principles calculations to investigate how alkali-metal adsorption, specifically cesium on bismuth films, deforms surface and bulk electronic bands, revealing the underlying charge-density correlations.

Contribution

It introduces a simple method to evaluate alkali-metal induced band deformation and clarifies the different behaviors of surface versus bulk bands upon alkali-metal adsorption.

Findings

Surface band deformation correlates with vertical charge-density profiles.

Bulk band shifts follow a rigid-band-shift model.

Provides a holistic understanding of alkali-metal effects on electronic structures.

Abstract

Alkali-metal adsorption on the surface of materials is widely used for in situ surface electron doping, particularly for observing unoccupied band structures by angle-resolved photoemission spectroscopy (ARPES). However, the effects of alkali-metal atoms on the resulting band structures have yet to be fully investigated, owing to difficulties in both experiments and calculations. Here, we combine ARPES measurements on cesium-adsorbed ultrathin bismuth films with first-principles calculations of the electronic charge densities and demonstrate a simple method to evaluate alkali-metal induced band deformation. We reveal that deformation of bismuth surface bands is directly correlated with vertical charge-density profiles at each electronic state of bismuth. In contrast, a change in the quantized bulk bands is well described by a conventional rigid-band-shift picture. We discuss these two aspects of the band deformation holistically, considering spatial distributions of the electronic states and cesium-bismuth hybridization, and provide a prescription for applying alkali-metal adsorption to a wide range of materials.