Symmetrization of the Coulomb pairing potential by electron-phonon interaction
- PDF / 286,311 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 37 Downloads / 268 Views
DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Symmetrization of the Coulomb Pairing Potential by Electron–Phonon Interaction V. I. Belyavsky*, V. V. Kapaev, Yu. V. Kopaev, and D. I. Mikhailyan Lebedev Physics Institute, Russian Academy of Sciences, Leninsky pr. 53, Moscow, 119991 Russia *email: [email protected] Received December 27, 2011
Abstract—It is shown that the Coulomb superconducting pairing in systems with the Fermi contour nesting can be described by a quasionedimensional potential oscillating in real space. The supplement of this repul sive potential with an isotropic pairing attraction corresponding to the phonon superconductivity mechanism and including the effect of predominant forward scattering upon electron–phonon interaction leads to sym metrization of this potential and a considerable increase in the superconducting transition temperature. DOI: 10.1134/S1063776112060040
1. INTRODUCTION Soon after the discovery of hightemperature superconductivity [1], it was assumed that the unusual superconducting (SC) pairing in cuprates is based on an electron mechanism [2] and electron correlations can be described by the Hubbard model [3]. The SCpairing mechanism under repulsion was proposed soon after the development of the macro scopic Bardeen–Cooper–Schrieffer (BCS) [4] and Bogolyubov [5] theory considering the superconduc tivity of transition metals using the twoband model [6, 7]. Kohn and Luttinger [8] showed that the SC pairing can be produced by the repulsive potential, which becomes negative in some finite region of real space. Such a property is inherent, for example, in the screened Coulomb potential in a degenerate Fermi gas, which exhibits Friedel oscillations. The Kohn–Luttinger mechanism [8] leads to the bound state of the relative motion of a pair of particles. The conclusion that under the pairing repulsion the main SC instability develops in the triplet p channel [9] was confirmed in the extended Hubbard model in the lowdensity limit [10]. Pairing in the p and d chan nels under repulsion usually corresponds to a low SC transition temperature Tc [11]. However, as argued in [12, 13], in the 2D system under singlet d pairing and population of the allowed band close to halffilling, even a weak onsite repulsion enhanced by band effects can considerably increase Tc despite the restric tion on SC pairing under Coulomb repulsion of elec trons in the p and d states [14]. The physical pairing mechanism in conventional superconductors is commonly attributed to electron– phonon interaction (EPI), in which the width of the layer of the effective attraction between electrons in the momentum space corresponds to the characteris
tic phonon energy εD = បωD, where ωD is the Debye frequency. If we assume that the superconductivity of cuprates corresponds to the phonon scenario and the role of the Coulomb interaction is reduced to “switch ing” of gap symmetry from swave to dwave symme try [15–18], then high Tc values can be obtained only for a rather high EPI coupling constant taking in
Data Loading...
