Microscopic quantum interference in excitonic condensation of Ta$_2$NiSe$_5$

TL;DR

This paper investigates the microscopic quantum interference phenomena in excitonic condensation of Ta$_2$NiSe$_5$, predicting specific experimental signatures such as coherence peaks and heat capacity jumps to validate the excitonic scenario.

Contribution

It provides a theoretical analysis of quantum interference effects and predicts observable experimental signatures in Ta$_2$NiSe$_5$ for excitonic condensation.

Findings

Coherence peak in ultrasonic attenuation below T_c

Rapid decrease in NMR relaxation rate below T_c

Jump in heat capacity and elastic constant at T_c

Abstract

The microscopic quantum interference associated with excitonic condensation in Ta$_2$NiSe$_5$ is studied in the BCS-type mean-field approximation. We show that in ultrasonic attenuation the coherence peak appears just below the transition temperature $T_{\rm c}$ whereas in NMR spin-lattice relaxation the rate rapidly decreases below $T_{\rm c}$; these observations can offer a crucial experimental test for the validity of the excitonic condensation scenario in Ta$_2$NiSe$_5$. We also show that the excitonic condensation manifests itself in a jump of the heat capacity at $T_{\rm c}$ as well as in softening of the elastic shear constant, in accordance with the second-order phase transition observed in Ta$_2$NiSe$_5$.