Anomalies in the temperature dependence of the anisotropic gap in high-T c superconductors

The effects of cobalt substitution on the thermal diffusivity of YBa2Cu3O7−δ superconductor

“…where d is the lattice parameter along the c-axis and f(t) is a function of various parameters describing the thermal conduction due to a 2D Bose gas of thermal acoustic plasmons and is defined as concepts of this model and the meaning of these various parameters are discussed in detail in [15]. We have previously [17] shown that this model gives a very good description of Xc(T) data for the samples investigated here.…”

“…However, the comparison between these models is not the main concern in this study; rather, we will attempt an investigation of the rise in ~:(T) by adopting one of them [15] that describes ~.~(T), below and above Tc, based on the existence of weakly damped collective electron excitations of Bose type with acoustic dispersion relation (acoustic plasmons) inside the superconducting gap. In this model the thermal conductivity can be calculated by the following equation;…”

“…In the superconducting state (T< T~), the estimation of t~(T) from ~,c(T) is not a simple task since there are different theoretical models that can be used to determine ~.~(T), [15,[20][21][22]. However, the comparison between these models is not the main concern in this study; rather, we will attempt an investigation of the rise in ~:(T) by adopting one of them [15] that describes ~.~(T), below and above Tc, based on the existence of weakly damped collective electron excitations of Bose type with acoustic dispersion relation (acoustic plasmons) inside the superconducting gap.…”

“…In this paper we have investigated the role of the Cu-O chains on the thermal response of YBa2Cu307-6 using the recently developed transient-plane-source (TPS technique [14] to perform simultaneous measurements of thermal conductivity and diffusivity on YBa2Cu3 -xCoxO7-6, (x = 0.0, 0.1 ), over the temperature range from 35 to 300 K. The aim of this work is to study the influence of cobalt substitution on thermal diffusivity of YBa2Cu3OT-a, which may contribute to an understanding of possible relations between the structure modifications and the superconductivity mechanism in this compound. In order to reveal the contributions of phonons and charge-carrier contributions to ~c(T) in YBa2Cu307-6, we analyze the results in the framework of a recent theoretical model [15] based on acoustic plasmons. The phonon contribution to x(T) was estimated using conventional formulas for heat conduction in metals.…”

Langmuir vacuum and superconductivity

“…Accord ing to formula (1), the role of Coulomb repulsion increases progressively as the plasma density decreases and the plasma permittivity tends to unity. Analysis based on formula (1) naturally leads to the consideration of the low frequency range of the elec tromagnetic spectrum [4] and application of models assuming a linear [5] or quasilinear [6,7] dependence of the phonon frequency on the wavenumber k. In the context of the problem of high temperature supercon ductivity, the discrete Hubbard model [8,9] has been…”