Dipolon Theory of Thermal Conductivity and Muon Spin Relaxation Rates in High Critical Temperature Superconductors.
Abstract
First calculations of the electronic thermal conductivities kappa_{e} and muon spin relaxation rates sigma_mu have been performed in the framework of the dipolon mechanism of pairing considering quasiparticle energy and temperature dependent scattering meanlifetimes due to dipolons, oxygen vacancies, and phonons for the YBa _2Cu_3O_{7{}delta } system. The dipolonmechanism explains the experimental T_{c} (and also Delta) and T_ {c} versus the number of oxygen vacancies delta in the superconducting system YBa_2Cu_3O_{7{ }delta}. It means that the superconducting condensed state is explained by the dipolon theory. In our calculations one needs the values of T_ {c} and Delta which are thus known from the dipolon theory. Our calculations of the thermal conductivity for the YBa_2Cu_3O_{6.95 } system as a function of temperature in comparison with the experimental results show that it is essential to include scattering from dipolons and phonons. Vacancy scattering is not found to contribute importantly to the thermal conductivity. This is explained physically by the fact that the thermal currents are carried by the quasiparticle excitations in the superconducting planes whereas the oxygen vacancies are present only in the b chains and are not available for the scattering of quasiparticle excitations. We have performed calculations of the muon spin relaxation rates for the YBa_2Cu_3O _{7{}delta} system as a function of critical temperature T_ {c} at T=0 considering scattering by dipolons, oxygen vacancies, and phonons. The calculated results are then compared with experimental results. In the case of calculating the muon spin relaxation rates it is found essential to include the effect of a small number of vacancies to explain the experimental results. This can be explained by noting that the magnetic flux vortices redistribute the superconducting currents from the superconducting planes and some of these electrons then scatter off of the oxygen vacancies. We find that the electron scattering by dipolons is essential for explaining both the electronic thermal conductivities kappa_{e} and the muon spin relaxation rates sigma _mu..
 Publication:

Ph.D. Thesis
 Pub Date:
 1996
 Bibcode:
 1996PhDT........28B
 Keywords:

 Physics: Condensed Matter