Excitonic Instability Revealed by the Elastocaloric Effect in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$

Author(s): Elliott Rosenberg, Joss Ayres-Sims, Andrew Millis, David Cobden, and Jiun-Haw Chu Elastocaloric effect measurements on Ta2NiSe5 show that its phase transition at ~324 K is driven by a nonacoustic instability, rather than by an acoustic shear mode, strengthening the case that the transition is largely excitonic in nature. [Phys. Rev. Lett. 136, 046503] Published Wed Jan 28, 2026