Oussena, M., de Groot, P.A.J., Gagnon, R. and Taillefer, L.
Lock-in oscillations in magnetic hysteresis curves of YBa2Cu3O7-x single crystals
Physical Review Letters, 72, (22), . (doi:10.1103/PhysRevLett.72.3606).
We report the first direct experimental evidence of intrinsic pinning in hysteresis loops of untwinned YBa2Cu3O7-x single crystals, for magnetic fields perpendicular to the c axis. We have observed oscillations in the M-H loops that are well explained when one considers the layered structure of this compound. The oscillations are found to be periodic in H-1/2a and are induced by a succession of transitions between states for which the vortex lattice is commensurate with the crystal lattice periodicity in the direction perpendicular to the CuO2 planes. The following anisotropy parameters were extracted from the experimental results: Gamma cb=(mc/mb)1/2=6.3, Gamma ca=(mc/ma)1/2=5.6, and Gamma ab=(ma/mb)1/2=1.13.
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