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

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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Cited by in corpus (3)

• Ab initio Approach to Collective Excitations in Excitonic Insulators
• Long-lived relaxation channel and exciton-phonon coupling in Ta2NiSe5 via non-degenerate pump-probe spectroscopy
• Excitons and Optical Response in Excitonic Insulator Candidate TiSe${}_2$