The in-plane and cross-plane thermal conductivity of RBa 2 Cu 3 O 7−x (R = Eu, Gd, Dy, Er, Y) superconductors

Abstract

We present an analysis of thermal conductivity of a series of rare earth substituted high temperature superconductors (HTS) of the form RBa 2 Cu 3 O 7−x (R = Eu, Gd, Dy, Er, Y). Interaction of lattice vibrations with structural defects, surface boundaries, dislocations or point defects, phonons and electrons can lead to substantial thermal resistance. This work deals with the combined impact of all these scattering processes on the thermal conductivity of these HTSs and thus, presents a complete picture. The role of various scattering processes in thermal transport has been explored based on the many-body quantum dynamics for the bulk material. We have tried to interpret which scattering processes are important in different temperature ranges. We note that the boundary scattering is the sole contributor to thermal resistance at very low temperatures, in excellent agreement with experimental observations. Further, we also studied the anisotropic nature of thermal conductivity in single-crystal YBCO. Our results bear excellent agreement with the available experimental data for both the in-plane and cross-plane thermal conductivity. It is observed that the in-plane thermal conductivity is much higher than the cross-plane thermal conductivity imparting a 2 − D nature to the thermal transport in such materials. We conclude that of the various scattering processes, anisotropy in the thermal transport is largely owing to the defect scattering, phonon-phonon scattering and interference scattering processes. Such an analysis addresses the possibility of limiting the heat flow in a particular direction while allowing it in the other; a feature that can be exploited for the development of exotic technological high-temperature superconductor crystals for industrial use.