On Migdal's theorem and the pseudogap

Abstract

We study a model of quasiparticles on a two-dimensional square lattice coupled to Gaussian distributed dynamical molecular fields. The model describes quasiparticles coupled to spin or charge fluctuations, and is solved by a Monte Carlo sampling of the molecular field distributions. When the molecular field correlations are sufficiently weak, the corrections to the self-consistent Eliashberg theory do not bring about qualitative changes in the quasiparticle spectrum. But for a range of model parameters near the magnetic boundary, we find that Migdal's theorem does not apply and the quasiparticle spectrum is qualitatively different from its mean-field approximation, in that a pseudogap opens in the quasiparticle spectrum. An important feature of the magnetic pseudogap found in the present calculations is that it is strongly anisotropic. It vanishes anlong the diagonal of the Brillouin zone and is large near the zone boundary. In the case of ferromagnetic fluctuations, we also find a range of model parameters with qualitative changes in the quasiparticle spectral function not captured by the one-loop approximation, in that the quasiparticle peak splits into two. We provide intuitive arguments to explain the physical origin of the breakdown of Midgal's theorem

revised version

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• Anomalous self-energy and Fermi surface quasi-splitting in the vicinity of a ferromagnetic instability
• Anomalous pseudogap and superconducting state properties of heavily disordered Y1-xCaxBa2(Cu1-yZny)3O7-delta
• A spectral function tour of electron-phonon coupling outside the Migdal limit
• Magnetic mechanism of quasiparticle pairing in hole-doped cuprate superconductors
• Electronic self-energy and triplet pairing fluctuations in the vicinity of a ferromagnetic instability in 2D systems: the quasistatic approach
• Anisotropy of electronic correlations: On the applicability of local theories to layered materials
• Pseudogap and Superconducting Fluctuation in High-Tc Cuprates: Theory beyond 1-loop Approximation
• Two-Particle-Self-Consistent Approach for the Hubbard Model
• Diagrammatic perturbation theory and the pseudogap