Measurement of Electronic Structure and Surface Reconstruction in the Superionic Cu2-xTe

TL;DR

This study investigates the electronic structure and surface reconstruction of Cu2-xTe using ARPES and STM/STS, revealing a persistent 2x2 surface reconstruction and its relation to Cu ion deficiency, informing thermoelectric property understanding.

Contribution

It provides the first detailed analysis of Cu2-xTe's electronic structure and surface reconstruction, linking surface phenomena to thermoelectric behavior.

Findings

Observation of a 2x2 surface reconstruction surviving up to room temperature.

Identification of multiple surface reconstruction patterns related to Cu deficiency.

Electronic structure consistent with theoretical calculations, revealing impurity levels.

Abstract

Recently, layered copper chalcogenides Cu2X family (X=S, Se, Te) has attracted tremendous research interests due to their high thermoelectric (TE) performance, which is partly due to the superionic behavior of mobile Cu ions, making these compounds phonon liquids. Here, we systematically investigate the electronic structure and its temperature evolution of the less studied single crystal Cu2-xTe by the combination of angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscope/spectroscopy (STM/STS) experiments. While the band structure of the Cu2-xTe shows agreement with the calculations, we clearly observe a 2 * 2 surface reconstruction from both our low temperature ARPES and STM/STS experiments which survives up to room temperature. Interestingly, our low temperature STM experiments further reveal multiple types of reconstruction patterns, which suggests the origin of the surface reconstruction being the distributed deficiency of liquid-like Cu ions. Our findings reveal the electronic structure and impurity level of Cu2Te, which provides knowledge about its thermoelectric properties from the electronic degree of freedom.