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Interplane Cooper Pairing in YBa 2 Cu 3 O 7 Crystals and Phonon Frequency Softening Below T c as a Consequence of Electron‐Phonon Interaction
Author(s) -
Liaptsev A. V.
Publication year - 1992
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221690226
Subject(s) - pairing , phonon , hamiltonian (control theory) , condensed matter physics , chemistry , softening , electron , vibronic coupling , superconductivity , physics , crystal (programming language) , atomic orbital , atomic physics , quantum mechanics , molecule , mathematics , mathematical optimization , computer science , programming language
Abstract A model of the YBaCuO crystal based on tight‐binding approximation is considered. The electronic Hamiltonian describes uncoupled plane (layer) bands and chain bands. The vibronic interaction appears due to the overlap of Cu2(d x 2 – y 2) and O4(p z ) orbitals when the nuclei are displaced from their equilibrium positions. This interaction is transformed to the Renner‐type vibronic interaction which is nondiagonal with respect to the indices corresponding to different planes and quadratic in the vibronic coordinates. It is shown that the Renner‐type interaction can cause interplane pairing of electrons and phonon frequency softening below T c . Some estimates are obtained and compared with experimental data.