Mechanical measurement of vortex phase transition in YBa2Cu3O7+δ

Using the vibrating-reed technique, the internal friction (IF) Q-1 and modulus as functions of temperature were measured for a YBa2Cu3O7+δ single crystal at low applied magnetic fields up to 0.5 T. The frequency dependence of the IF related to the vortex is reported. No obvious shift of the IF peak position can be observed by varying the measurement frequency ranging from 102 to 103Hz but the IF peak height satisfies a power law Q-1∝ω-n (1<n<2). This is speculated to originate from a phase transition associated with the melting or a glass transition of the vortex lattice. These results provide a fundamental measurement of the phase diagram of vortices in high-Tc superconductors. copyright 1997 The American Physical Society