Surface properties of SmB6 from x-ray photoelectron spectroscopy

TL;DR

This study uses x-ray photoelectron spectroscopy to analyze the surface properties of SmB6 crystals, revealing temperature-dependent surface shifts, valence states, and surface chemistry complexities, but does not clarify the origin of its surface conductivity.

Contribution

The paper provides detailed surface characterization of SmB6, highlighting temperature effects, valence states, and surface chemistry, contributing to understanding its surface phenomena.

Findings

Surface core level shift vanishes at higher temperatures

Sm valence is between 2.5 and 2.6

Surface B/Sm ratio exceeds stoichiometric value

Abstract

We have investigated the properties of cleaved SmB$_6$ single crystals by x-ray photoelectron spectroscopy. At low temperatures and freshly cleaved samples a surface core level shift is observed which vanishes when the temperature is increased. A Sm valence between 2.5 - 2.6 is derived from the relative intensities of the Sm$^{2+}$ and Sm$^{3+}$ multiplets. The B/Sm intensity ratio obtained from the core levels is always larger than the stoichiometric value. Possible reasons for this deviation are discussed. The B $1s$ signal shows an unexpected complexity: an anomalous low energy component appears with increasing temperature and is assigned to the formation of a suboxide at the surface. While several interesting intrinsic and extrinsic properties of the SmB$_6$ surface are elucidated in this manuscript no clear indication of a trivial mechanism for the prominent surface conductivity is found.