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Observation of an amplitudelike mode in the excitonic insulator Ta2Pd3Te5

Y.-S. Choi1, Dirk Wulferding2,*, Raju Kalaivanan3, Rajesh Kumar Ulaganathan4, Raman Sankar3,†, and Kwang-Yong Choi1,‡

  • *Contact author: d.wulferding@sejong.ac.kr
  • †Contact author: sankarndf@gmail.com
  • ‡Contact author: choisky99@skku.edu
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Phys. Rev. Research 8, 023273 – Published 10 June, 2026

DOI: https://doi.org/10.1103/2swg-p1pn

Abstract

The excitonic insulator candidate Ta2Pd3Te5 has emerged as a promising platform to explore macroscopic quantum condensation and its collective excitations. Using polarization-resolved Raman spectroscopy, we identify a symmetry-selective electronic mode that softens and undergoes linewidth renormalization across the characteristic temperature T*∼100K. This mode, most prominent in the B3g channel, is assigned to vestigial collective excitations associated with excitonic correlations, as evidenced by its order-parameter-like temperature evolution and symmetry dependence. In parallel, a damped Drude-like response exhibits a suppressed scattering rate and maximum intensity at T*, while phonon intensities display symmetry-dependent anomalies, signaling anisotropic band reconstructions and the spontaneous opening of a collective condensation gap. These observations provide compelling spectroscopic evidence for collective amplitude excitations in Ta2Pd3Te5, establishing this material as a bulk excitonic insulator.

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Corrections

26 June, 2026

Correction: The second affiliation contained errors and has been fixed.

Article Text

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Outline

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Phys. Rev. Research 8, 023273– Published 10 June, 2026
  • Received 7 September 2025
  • Accepted 19 May 2026
  • Corrected 26 June 2026
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