Screening induced crossover between phonon- and plasmon-mediated pairing in layered superconductors

Abstract

Two-dimensional (2D) metals can host gapless plasmonic excitations that strongly couple to electrons and thus may significantly affect superconductivity. To investigate the dynamical interplay of the electron–electron and electron–phonon interactions in the theory of 2D superconductivity, we apply a full momentum- and frequency-dependent one-loop theory treating electron–phonon, electron–plasmon, and phonon–plasmon coupling with the same accuracy. We tune the strength of the Coulomb interaction by varying the external screening ε e x t to the layered superconductor and find three distinct regions. At weak screening, superconductivity is mediated by plasmons. In the opposite limit conventional electron–phonon interactions dominate. In between, we find a suppressed superconducting state. Our results show that even in conventional electron–phonon coupled layered materials, superconductivity can be significantly enhanced by the electron–plasmon coupling in a manner that can be controlled by the external screening.

D-Wave Superconducting Gap Symmetry as a Model for Nb1−xMoxB2 (x = 0.25; 1.0) and WB2 Diborides

“…Another purely theoretical possibility exists for a crossover between the electronphonon and the electron-plasmon mediated pairing in layered superconductors. This possibility was recently proposed by in 't Veld et al [97]. This is another possibility that shows how high-pressure (which, as a rule, changes the screening length in the compound) can induce the change in the pairing symmetry from s-wave (which is widely considered to be a consequence of the electron-phonon interaction) to nodal symmetry (which is widely accepted to be attributed to non-electron-phonon mediated pairing).…”