Unconventional strain dependence of superconductivity in spin-triplet superconductor Sr2RuO4

Ultrasonic measurements have been performed on high quality single crystals of Sr2RuO4 across the superconducting transition temperature T-c (approximate to 1.37 K). A discontinuous jump at T-c was observed in a longitudinal elastic modulus C-11 as is seen in conventional superconductors. and the strain dependence of T-c was estimated from the jump by using the Ehrenfest relation. The uniaxial pressure dependence of T-c in Sr2RuO4 was found to be negative along the a axis and positive along the c axis, respectively. Thermodynamic analysis has cleanly shown that the superconductivity of Sr2RuO4 is much affected by the deformation of RuO2 planes. The strain effects on Superconductivity are explained by large anisotropy of the lattice and electronic structure in Sr2RuO4.