Fate of the excitonic insulator in the presence of phonons

Abstract

The influence of phonons on the formation of the excitonic insulator has hardly been analyzed so far. Recent experiments on $\mathrm{T}{\mathrm{a}}_2\mathrm{NiS}{\mathrm{e}}_5$, 1$T$-$\mathrm{TiS}{\mathrm{e}}_2$, and $\mathrm{TmS}{\mathrm{e}}_{0.45}\mathrm{T}{\mathrm{e}}_{0.55}$, being candidates for realizing the excitonic-insulator state, suggest, however, that the underlying lattice plays a significant role. Employing the Kadanoff-Baym approach we address this issue theoretically. We show that owing to the electron-phonon coupling a static lattice distortion may arise at the excitonic instability. Most importantly such a distortion will destroy the acoustic phase mode being present if the electron-hole pairing and condensation is exclusively driven by the Coulomb interaction. The absence of off-diagonal long-range order, when lattice degrees of freedom are involved, challenges that excitons in these materials form a superfluid condensate of Bose particles or Cooper pairs composed of electrons and holes.

14 pages, 4 figures, final version

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Cited by in corpus (20)

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• Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in 1$T$-TiSe${}_2$
• Charge-density wave induced by combined electron-electron and electron-phonon interactions in 1$T$-TiSe${}_2$: A variational Monte Carlo study
• Bulk Photovoltaic Effect Driven by Collective Excitations in a Correlated Insulator
• Photo-induced phase transition and associated time scales in the excitonic insulator Ta${}_2$NiSe${}_5$
• A New Era of Excitonic Insulators
• Unveiling the underlying interactions in Ta2NiSe5 from photo-induced lifetime change
• Signatures of ultrafast reversal of excitonic order in Ta${}_2$NiSe${}_5$
• Disentangling lattice and electronic instabilities in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ by nonequilibrium spectroscopy
• Electric and magnetic multipoles and bond orders in excitonic insulators
• Finite-temperature photoemission in the extended Falicov-Kimball model: a case study for Ta${}_2$NiSe${}_5$
• Optical signatures of exciton-polarons from diagrammatic Monte Carlo
• Third-harmonic generation in excitonic insulators
• Excitonic insulators and Gross-Neveu models
• Excitonic Tunneling in the AB-bilayer Graphene Josephson Junctions
• Detecting photoelectrons from spontaneously formed excitons
• Photo-induced Dynamics of Quasicrystalline Excitonic Insulator
• Unconventional excitonic insulators in two-dimensional topological materials
• Probing the collective excitations of excitonic insulators in an optical cavity
• Ab initio Approach to Collective Excitations in Excitonic Insulators