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arXiv · 2403.18083

Collective modes and Raman response in Ta$_2$NiSe$_5$

Banhi Chatterjee·Jernej Mravlje·Denis Golež
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Abstract

We explore the collective response in an excitonic insulator phase in Ta$_2$NiSe$_5$ 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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Banhi Chatterjee, Jernej Mravlje, Denis Golež. 2024-03-26. Collective modes and Raman response in Ta$_2$NiSe$_5$. https://doi.org/10.1103/physrevb.111.l121106

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