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.

arXiv comment14 pages, 4 figures, final version

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Cited by in corpus (40)

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• Giant exciton Fano resonance in quasi-one-dimensional Ta${}_2$NiSe${}_5$
• Direct observation of excitonic instability in Ta2NiSe5
• Photo-induced enhancement of excitonic order
• Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in 1$T$-TiSe${}_2$
• Band hybridisation at the semimetal-semiconductor transition of Ta${}_2$NiSe${}_5$ enabled by mirror-symmetry breaking
• Photo-induced gap closure in an excitonic insulator
• Non-Coulomb strong electron-hole binding in $T{a}_{2}NiS{e}_5$ revealed by time- and angle-resolved photoemission spectroscopy
• Inhibition of the photoinduced structural phase transition in the excitonic insulator Ta${}_2$NiSe${}_5$
• Imaging the coherent propagation of collective modes in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ at room temperature
• Collective Modes in Excitonic Insulators: Effects of Electron-Phonon Coupling and Signatures in Optical Response
• Heterobilayers of 2D materials as a platform for excitonic superfluidity
• Orthorhombic-to-monoclinic transition in Ta${}_2$NiSe${}_5$ due to a zone-center optical phonon instability
• Charge-density wave induced by combined electron-electron and electron-phonon interactions in 1$T$-TiSe${}_2$: A variational Monte Carlo study
• Pump driven normal-to-excitonic insulator transition: Josephson oscillations and signatures of BEC-BCS crossover in time-resolved ARPES
• Competition between excitonic charge and spin density waves: Influence of electron-phonon and Hund's rule couplings
• 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${}_5$
• Nonlinear spectroscopy of collective modes in excitonic insulator
• A New Era of Excitonic Insulators
• Nonequilibrium dynamics in the pump-probe spectroscopy of excitonic insulators
• 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
• Unveiling the underlying interactions in Ta2NiSe5 from photo-induced lifetime change
• Electric and magnetic multipoles and bond orders in excitonic insulators
• Collective excitations of the U(1)-symmetric exciton insulator in a cavity
• 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
• Excitonic condensation reflecting electronic states in two-band Penrose-Hubbard model
• Third-harmonic generation in excitonic insulators
• Exciton-Peierls mechanism and universal many-body gaps in carbon nanotubes
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• Excitonic Josephson effect in double-layer graphene junctions
• Excitonic Tunneling in the AB-bilayer Graphene Josephson Junctions
• Detecting photoelectrons from spontaneously formed excitons
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• Unconventional excitonic insulators in two-dimensional topological materials
• Ab initio Approach to Collective Excitations in Excitonic Insulators
• Probing the collective excitations of excitonic insulators in an optical cavity