Electronic band structure in pristine and Sulfur-doped Ta$_2$NiSe$_5$

TL;DR

This study investigates how Sulfur doping affects the electronic band structure and excitonic insulating phase of Ta$_2$NiSe$_5$, revealing phase suppression at high doping levels and three-dimensional electronic characteristics.

Contribution

It provides the first detailed angle-resolved photoemission analysis of Sulfur-doped Ta$_2$NiSe$_5$, highlighting the evolution of its electronic structure and phase stability with doping.

Findings

Excitonic phase persists at 25% S-doping

Phase is heavily suppressed at 50% S-doping

Electronic structure shows three-dimensionality

Abstract

We present an angle-resolved photoemission study of the electronic band structure of the excitonic insulator Ta$_2$NiSe$_5$, as well as its evolution upon Sulfur doping. Our experimental data show that while the excitonic insulating phase is still preserved at a Sulfur-doping level of 25$\%$, such phase is heavily suppressed when there is a substantial amount, $\sim$ 50$\%$, of S-doping at liquid nitrogen temperatures. Moreover, our photon energy-dependent measurements reveal a clear three dimensionality of the electronic structure, both in Ta$_2$NiSe$_5$ and Ta$_2$Ni(Se$_{1-x}$S$_x$)$_5$ ($x=0.25, 0.50$) compounds. This suggests a reduction of electrical and thermal conductivities, which might make these compounds less suitable for electronic transport applications.