COUPLED STATES IN ELECTRON–PHONON SYSTEM, SUPERCONDUCTIVITY AND HIGH T_c SUPERCONDUCTIVITY OF CRYSTALS

Abstract

The new theoretical approach is proposed for studying the coupled states responsible for superconductivity in crystal without using the idea of electron pairing. From our approach it follows that BCS electron-pairing postulates are only approximate. It is shown that superconductivity (SC) coupled states can be created by pairs of electrons with nonzero full momentum and spin (k1 + k2 ≠ 0, s + s' ≠ 0). The model numerical calculations have shown that dependence of SC gap (energy of coupled states) on temperature is nonexponential and depends on the momenta of electrons in pair.

N‐band Hubbard models. III. Boson–fermion and interaction–boson models for high‐Tc superconductivity

“…The MB effect for HTSC has been theoretically examined by several groups 20, 21, 67, 82, 83 on the basis of model Hamiltonians. Here, we do not repeat such microscopic theories.…”

Multiband Superconductivity

“…In this subsection, we will use the two-particle Green's function [18][19][20] to investigate the physical properties of superconductivity in a two-band model. Firstly, let us define the one-particle Green's functions:…”

“…If the coupling constant of e-e interaction (renormalized by electron-phonon interaction) becomes negative, coupled states will appear in the electronic system. In previous papers, [18][19][20] we have presented the analysis of the spectral properties of two-particle Green function. According to the same procedure, 18-20 we obtain the equation for coupled states in the electronic system:…”

“…According to the procedure given earlier, [18][19][20] we study the situation near the extremum (minimum or maximum) of the electron zone. We suppose k = k = k 0 + k and ε ν k0 = ε ν corresponds to the extremum of zone.…”

“…[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] Within the framework of two-particle Green function, 18 it is shown that in the electron-phonon system there exists a new class of so-called coupled states. Numerical calculations have shown that superconducting (SC) gap depends on the number of bands crossing the Fermi level and on the momenta k 1 + k 2 = 0 of the interacting electrons.…”