{\mu}-PES Studies on TiNCl and Quasi-two-dimensional Superconductor Na-intercalated TiNCl

TL;DR

This study used micro-photoemission spectroscopy to investigate the electronic structure changes in TiNCl and Na-intercalated TiNCl, revealing increased metallic character and strong electron correlation effects upon doping.

Contribution

First application of {}-PES to electron-doped TiNCl, showing deviations from rigid band behavior and highlighting the role of electron correlations.

Findings

Na-intercalation enhances metallic spectral features.

Na-TiNCl exhibits strong electron correlation effects.

{}-PES effectively probes electronic structures of small samples.

Abstract

Electron-doped TiNCl is a superconductor, for which exotic mechanisms of the superconductivity have been discussed. However, difficulty in preparing large single-phase samples has prevented the direct observation of its electronic structure and how that changes with electron doping. In this study, micro-photoemission spectroscopy ({\mu}-PES) was used to reveal the electronic structures of TiNCl and Na-intercalated TiNCl (Na-TiNCl). Comparison of Ti 2p core-level spectra shows the enhancement of a spectral feature in Na-TiNCl that suggests an increase in its metallic character. This indicates the introduction of electron carriers to the TiNCl layers. Although the overall valence band electronic structure of parent TiNCl could be reproduced by first-principle calculations, that of Na-TiNCl showed a marked deviation from the rigid band model near the Fermi level (EF). The spectral shape observed near EF of Na-TiNCl was found to be similar to a result in early transition metal oxides that has been attributed to the effect of strong electron correlation. The present study also demonstrated the usefulness of {\mu}-PES to obtain reliable electronic structure data for samples that are difficult to make at large sizes.