Shear-modulus change belowTcin YBa2Cu3O7−x

Abstract

The ultrasonic transverse-wave velocity in the high-Tcmetal-oxide superconductor YBa2Cu3O7−xbetween 275 and 4 K was measured. AboveTcthe velocity shows normal behavior: during cooling, it displays a monotonic increase with decreasing slope. During cooling belowTcthe shear modulus departs from normal behavior, increasing as ΔG /G=b[1 − (T/Tc)n, wheren= 3. These results depart dramatically from those expected for a simple second-order normal-superconducting phase transition.