Vortex lock-in transition coinciding with the 3D to 2D crossover in YBa2Cu3O7

Abstract

A vortex lock-in transition was directly detected by torque magnetometry in an overdoped YBa 2 Cu 3 O 7 single crystal of low anisotropy (≈ 7). The locked-in state was observed below the two-to three-dimensional crossover temperature T cr = 76 K, independently of extrinsic pinning effects, thanks to a high-quality clean crystal and the use of a vortex shaking technique. The lock-in effect is enhanced by decreasing temperature and increasing magnetic field. The shape of the torque signal as a function of the angle between the applied magnetic field and the crystallographic c axis is in very good agreement with the model developed by Feinberg and Ettouhami [Int. J. Mod. Phys. B 7, 2085 (1993)] for quasi-2D superconductors, despite the low anisotropy of the material.