Nonadiabatic superconductivity: The role of van Hove singularities

Journal Article · Mon Jan 01 04:00:00 EST 1996 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.53.932· OSTI ID:434525

Cappelluti, E; Pietronero, L ^[1]

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1. Dipartimento di Fisica, Universita di Roma La Sapienza, Piazzale Aldo Moro 2, I-00185 Roma (Italy)

We consider the effect of van Hove singularities in the density of states (DOS) on the generalized theory of superconductivity that includes the first contribution beyond Migdal{close_quote}s theorem (nonadiabatic). Most of our results are not specific to a van Hove singularity and can be extended to the generic situation in which the Fermi surface is close to a peak in the DOS. Often the effect of a peak in the DOS is discussed in terms of an enhancement of the electron-phonon coupling {lambda} using the standard theory. Here we point out that in the most interesting situations this peak structure unavoidably leads to a breakdown of Migdal{close_quote}s theorem because the effective range of electronic energies becomes very narrow. We include therefore the first diagrams beyond Migdal{close_quote}s theorem that lead to a change in the structure of the theory and not just on the value of the effective coupling. These nonadiabatic effects lead naturally to an enhancement of the value of {ital T}{sub {ital c}} with respect to the adiabatic theory with the same coupling. This enhancement is mainly due to the predominant role of small momentum scattering that is a consequence of the peak in the DOS. These results provide therefore a perspective for the effects of DOS peaks in the theory of superconductivity. {copyright} {ital 1996 The American Physical Society.}

• OSTI ID: 434525
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 2 Vol. 53; ISSN PRBMDO; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ELECTRON-PHONON COUPLING
ELECTRONIC STRUCTURE
ENERGY-LEVEL DENSITY
MIGDAL THEORY
SINGULARITY
SUPERCONDUCTORS