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

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 $T_{\mathrm{c}}$ whereas in NMR spin-lattice relaxation the rate rapidly decreases below $T_{\mathrm{c}}$; 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 $T_{\mathrm{c}}$ as well as in softening of the elastic shear constant, in accordance with the second-order phase transition observed in Ta${}_2$NiSe${}_5$.

5 pages, 3 figures, Supplemental Material