Collective modes and Raman response in Ta₂NiSe₅

2024/03/26 by Banhi Chatterjee, Chatterjee, Banhi, Jernej Mravlje +3
Engineering · Materials Science · #2D Materials and Applications #Chalcogenide Semiconductor Thin Films #FOS: Physical sciences #Molecular Junctions and Nanostructures #Strongly Correlated Electrons (cond-mat.str-el)

paper · pdf · doi:10.48550/arxiv.2403.18083

openalex publication_date 2024/03/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

We explore the collective response in an excitonic insulator phase in Ta₂NiSe₅ using a semirealistic model including relevant lattice and electronic instabilities. We calculate order-parameter susceptibility and Raman response within a time-dependent Hartree-Fock approach. Contrary to the standard expectations, the amplitude mode frequency does not coincide with the single-particle gap but has a higher frequency. We find a phase mode that is massive because the excitonic condensation breaks a discrete symmetry only and that becomes heavier as the electron-lattice coupling is increased. These features are expected to apply to generic realistic excitonic insulators. We discuss scenarios under which the phase mode does not appear as a sharp in-gap resonance.

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