Anisotropic stress dependence of Tc in YBa2Cu3O7−δ single crystals deduced from thermal expansion, measured with a capacitive quartz-dilatometer

Abstract

Abstract High resolution thermal expansion measurements were carried out on twinned and monodomain YBa 2 Cu 3 O 7−δ single crystals in the temperature range from 15 to 300 K. At the superconducting transition temperature T c anisotropic jumps of the thermal expansion coefficient α( T ) were observed along all three crystal axes. The monodomain crystal exhibits opposite signs of the jumps Δα in the a and b directions leading to the conclusion that a tetragonal lattice in YBa 2 Cu 3 O 7−δ favours superconductivity. Utilizing data for the specific heat, the uniaxial stress and strain dependence of T c is calculated. The uniaxial stress dependence is also found to be highly anisotropic leading to a small hydrostatic pressure dependence of 0.03 K/kbar for the monodomain sample.