Fate of the excitonic insulator in the presence of phonons

B. Zenker, H. Fehske, and H. Beck
Phys. Rev. B 90, 195118 – Published 11 November 2014

Abstract

The influence of phonons on the formation of the excitonic insulator has hardly been analyzed so far. Recent experiments on Ta2NiSe5,1TTiSe2, and TmSe0.45Te0.55, 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.

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  • Received 17 July 2014
  • Revised 15 October 2014

DOI:https://doi.org/10.1103/PhysRevB.90.195118

©2014 American Physical Society

Authors & Affiliations

B. Zenker1, H. Fehske1, and H. Beck2

  • 1Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, D-17489 Greifswald, Germany
  • 2Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, CH-1700 Fribourg, Switzerland

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Issue

Vol. 90, Iss. 19 — 15 November 2014

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