Anisotropic uniaxial-stress dependence of the superconducting transition temperature in single crystals of κ-(BEDT-TTF)2Cu[N(CN)2]Br

Abstract High-resolution linear thermal-expansion measurements on κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br single crystals along the three principal directions in the temperature range around the superconducting transition of T c = 11 K have been performed via capacitive dilatometry. Highly anisotropic jumps in the thermal-expansion coefficients α i are observed: Δα a >Δα c >Δα b . Using these data we calculate the uniaxial-stress dependence of T c which directly proves that the most critical parameter in this compound affecting the value of T c is the anion chain length and the related sulfur-sulfur orbital overlap between the donor molecules. In this compound we expect an increase of the superconducting transition temperature by elongation of the polymeric anion chain. Our deduced value for the hydrostatic-pressure dependence of T c is in excellent agreement with the literature data.