Phonon Dispersion and the Competition between Pairing and Charge Order

The Holstein model describes the interaction between fermions and a collection of local (dispersionless) phonon modes. In the dilute limit, the phonon degrees of freedom dress the fermions, giving rise to polaron and bipolaron formation. At higher densities, the phonons mediate collective supercondu...

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Bibliographic Details
Published in:Physical review letters 2018-05, Vol.120 (18), p.187003-187003, Article 187003
Main Authors: Costa, N C, Blommel, T, Chiu, W-T, Batrouni, G, Scalettar, R T
Format: Article
Language:English
Subjects:
Charge density waves
Competition
Computer simulation
Critical temperature
Curvature
Fermi surfaces
Fermions
Long range order
Nesting
Phase diagrams
Phonons
Physics
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Summary:The Holstein model describes the interaction between fermions and a collection of local (dispersionless) phonon modes. In the dilute limit, the phonon degrees of freedom dress the fermions, giving rise to polaron and bipolaron formation. At higher densities, the phonons mediate collective superconducting (SC) and charge-density wave (CDW) phases. Quantum Monte Carlo (QMC) simulations have considered both these limits but have not yet focused on the physics of more general phonon spectra. Here we report QMC studies of the role of phonon dispersion on SC and CDW order in such models. We quantify the effect of finite phonon bandwidth and curvature on the critical temperature T_{cdw} for CDW order and also uncover several novel features of diagonal long-range order in the phase diagram, including a competition between charge patterns at momenta q=(π,π) and q=(0,π) which lends insight into the relationship between Fermi surface nesting and the wave vector at which charge order occurs. We also demonstrate SC order at half filling in situations where a nonzero bandwidth sufficiently suppresses T_{cdw}.
ISSN:0031-9007
1079-7114
DOI:10.1103/physrevlett.120.187003