High-Q mechanical oscillator studies of single crystal YBa2Cu3O7−δ

Abstract

High-Q mechanical oscillator measurements obtained at low amplitude, equivalent to extremely low-field (microgauss) ac-susceptibility data, reveal subtle features in the vortex dissipation of YBa2Cu3O7−δ single crystals. These include an oscillatory modulation of vortex dissipation as a function of temperature forH}c. We find that the usually smooth, single-peaked dissipation behavior is a result of over-driving the sample (tilt oscillation amplitude greater than 10−6 radians); resolving the fine structure of the dissipation peaks requires very low amplitude (order of 10−7 radians) excitation. A simple and appealing explanation of the fine structure in terms of intrinsic pinning and the temperature dependence of the coherence length is presented. The fine structure was also observed to be enhanced for particular fields, reflecting the commensurability of the overall vortex lattice with the crystal lattice.