Stability of the superconducting state in YBa_2Cu_3O_7
Abstract
The nonadiabatic Heisenberg model (NHM) proposed as an extension of the Heisenberg model makes a contribution to the eigenstate problem of superconductivity. The Hamiltonian H^n derived within this group-theoretical model has superconducting eigenstates if and only if the considered material possesses a narrow, roughly half-filled "superconducting" energy band of special symmetry in its band structure. This paper shows that the high-temperature superconductor YBa_2Cu_3O_7 possesses such a superconducting band. This new result together with previous observations about other superconductors and non-superconductors corroborates the theoretical evidence within the NHM that stable superconducting states are connected with superconducting bands. It is proposed that the type of superconductivity, i.e., whether the material is a conventional low-T_c or a high-T_c superconductor, is determined by the energetically lowest boson excitations that carry the crystal spin 1*hbar and are sufficiently stable to transport this crystal spin-angular momentum through the crystal. This mechanism provides the electron-phonon mechanism that enters the BCS theory in conventional superconductors.
Keywords
Cite
@article{arxiv.0704.2110,
title = {Stability of the superconducting state in YBa_2Cu_3O_7},
author = {Ekkehard Krüger},
journal= {arXiv preprint arXiv:0704.2110},
year = {2011}
}