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arXiv · 2609.26485

Extraordinary Lifetime Enhancement of Coherent Phonon-Amplitude Modes in the Excitonic Insulator Phase of Ta2Pd3Te5

Anjan Kumar N M·Shuhan Wang·Snehashish Chatterjee·Yan Zhu·MinJae Kim·Tobias Ritschel·Elaheh Sadrollahi·Jochen Geck·Achim Rosch·Chandra Shekhar·Claudia Felser·Stefan Kaiser
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Abstract

The excitonic insulator (EI) is an electronic phase of condensed excitons. However, in many prototypical materials the presence of a concurrent structural transition complicates the identification of a purely electronic origin of the ordered state. Here, we investigate Ta2Pd3Te5, in which an EI phase develops below TC ~ 100 K in the absence of a detectable structural transition. We characterize the excitonic condensate via its coherent phonon-amplitude response. Most strikingly, an extraordinarily strong lifetime enhancement of these modes sets in below TC which we establish as a new and robust fingerprint linked to exciton condensation. We discuss possibilities to capture the enhancement when taking into account a coupling of excitonic and lattice effects in line with the coupled phonon-amplitude response. Within an order-parameter polaron picture coupling to the excitonic state may dress the phonon mode and thereby suppress its relaxation and a phenomenological model combines the anharmonic phonon response and a reduced electronic scattering due to the gap opening in the EI phase.

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Anjan Kumar N M, Shuhan Wang, Snehashish Chatterjee, Yan Zhu, MinJae Kim, Tobias Ritschel, Elaheh Sadrollahi, Jochen Geck, Achim Rosch, Chandra Shekhar, Claudia Felser, Stefan Kaiser. 2026-09-22. Extraordinary Lifetime Enhancement of Coherent Phonon-Amplitude Modes in the Excitonic Insulator Phase of Ta2Pd3Te5. https://arxiv.org/abs/2609.26485

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