Anisotropic resistivity and paraconductivity of Tl2Ba2CaCu2O8 single crystals.

Abstract

The anisotropic resistivity and paraconductivity of ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ single crystals were measured. The in-plane and c-axis resistivities are, respectively, \ensuremath{\sim}7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ and ${10}^{\mathrm{\ensuremath{-}}1}$ \ensuremath{\Omega} cm at room temperature. The c-axis resistivity decreases with decreasing temperature in the temperature range from room temperature down to the superconducting transition temperature, and the second derivative of ${\mathrm{\ensuremath{\rho}}}_{\mathit{c}}$ is negative, which is not characteristic of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2.2}$${\mathrm{Ca}}_{0.8}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8}$ single crystals, in which the second derivative is either positive or zero. The in-plane paraconductivity is obtained from the in-plane resistivity, and a method without the critical temperature as an adjustable parameter is employed to obtain the dimensionality. The data show that the superconductivity is two dimensional, but a crossover from two to three dimensions has also been observed near the transition temperature in some samples.