Thermal conductivity of impurity-doped high-Tcsuperconductors

Abstract

The thermal conductivity K(T) of polycrystalline ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{M}}_{\mathit{x}}$ ${)}_3$ ${\mathrm{O}}_7$ with M=Zn and Al (0≤x≤0.1) and ${\mathrm{Y}}_{1\mathrm{-}\mathit{y}}$ ${\mathit{R}}_{\mathit{y}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ with R=Pr and Gd (0≤y≤1.0) has been measured for temperatures 1.2≤T≤200 K. In the pure material, K(T) decreases slightly with decreasing temperature above ${\mathit{T}}_{\mathit{c}}$ and below ${\mathit{T}}_{\mathit{c}}$ there is a strong enhancement of K(T) reaching a maximum at ∼50 K followed by a sharp decrease. At temperatures below 10 K a ${\mathit{T}}^2$ dependence is evident similar to behavior reported for amorphous systems with glasslike phonon scattering on the tunneling states. Doping with Zn or Pr rapidly depresses ${\mathit{T}}_{\mathit{c}}$ and also depresses the maximum in K(T) even at concentrations that remain superconducting. This effect is observable to a lesser degree for the Al and Gd dopants. Comparisons between the K(T) behavior for impurities that do not depress ${\mathit{T}}_{\mathit{c}}$ with those that diversely alter the superconducting properties are presented together with an analysis of the data using the Tewordt-Wölkhausen (TW) theory.