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Electronic Tuning of the Soft-Phonon Transport Anomaly in Ta2Ni(SxSe1−x)5

Yuan-Shan Zhang1,*, Masahiko Isobe1, Hidenori Takagi1,2,3, and Dennis Huang1,†

  • *Contact author: Yuanshan.Zhang@fkf.mpg.de
  • †Contact author: D.Huang@fkf.mpg.de
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Phys. Rev. Lett. 137, 106503 – Published 2 September, 2026

DOI: https://doi.org/10.1103/l5xq-2yrt

Abstract

Ta2NiSe5 continues to be investigated for its phase transition at Tc=326  K, where it develops both an electronic gap and a distortion of its Ta/Ni chains. One intriguing feature at Tc seen in thermal transport is the giant anisotropic scattering of phonons moving perpendicular to the chains, which is apparently associated with the softening of a transverse acoustic phonon, but whose microscopic origin and significance demand clarification. By tuning the normal-state band overlap or gap with S substitution, we uncover a close connection between this soft-phonon transport anomaly and underlying electronic instabilities: when Ta2Ni(SxSe1−x)5 approaches a band insulator at high x, and signatures of the electronic transition are suppressed, the soft-phonon transport anomaly concomitantly vanishes. Our results establish the following picture for the Ta2Ni(SxSe1−x)5 family: near the S end, a sole lattice instability gives rise to a weak structural transition with Tc approaching 130 K. Near the Se end, additional electronic instabilities boost Tc up to 326 K and amplify experimental signatures of the transition. The strong interaction between electrons, holes, and the lattice is manifested as a soft-phonon transport anomaly accompanied by electronic fluctuations, which include excitonic and hybridization-gap fluctuations.

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Phys. Rev. Lett. 137, 106503– Published 2 September, 2026
  • Received 24 February 2026
  • Accepted 22 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

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