Theory of Orbital Susceptibility on Excitonic Insulator

TL;DR

This paper investigates how the orbital susceptibility of an excitonic insulator varies with temperature, revealing an anomalous enhancement linked to the excitonic gap, with calculations matching experimental data for Ta$_2$NiSe$_5$.

Contribution

It introduces a theoretical analysis of temperature-dependent orbital susceptibility in excitonic insulators, explicitly modeling Ta$_2$NiSe$_5$ and aligning with experimental observations.

Findings

Orbital susceptibility shows anomalous enhancement at certain temperatures.

Theoretical results agree with experimental measurements for Ta$_2$NiSe$_5$.

Additional orbital susceptibility arises due to the excitonic gap.

Abstract

We study the temperature dependence of the orbital susceptibility of an excitonic insulator on the basis of a two-band model. It is shown that a drastic change (an anomalous enhancement) in susceptibility as a function of temperature occurs owing to the occurrence of additional orbital susceptibility due to the excitonic gap. We calculate explicitly the temperature dependence of orbital susceptibility for a model of Ta$_2$NiSe$_5$, and show that the result is consistent with experimental results.