Peak effect in YBCO crystals: Statics and dynamics of the vortex lattice

Abstract

Oscillatory dynamics and quasi-static Campbell regime of the vortex lattice (VL) in twinned YBa2Cu3O7 single crystals has been explored at low fields near the peak effect (PE) region by linear and non-linear ac susceptibility measurements. We show evidence that the PE is a dynamic anomaly observed in the non-linear response, and is absent in the Labusch constant derived from the linear Campbell regime. Static properties play a major role however, and we identify two H(T) lines defining the onset and the end of the effect. At H1(T) a sudden increase in the curvature of the pinning potential wells with field coincides with the PE onset. At a higher field, H2(T), a sudden increase in linear ac losses, where dissipative forces overcome pinning forces, marks the end of Campbell regime and, simultaneously, the end of the PE anomaly. Vortex dynamics was probed in frequency dependent measurements, and we find that in the PE region, vortex dynamics goes beyond the description of a power law with a finite creep exponent for the constitutive relation.

arXiv comment8 pages, 5 figures

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• Ordered, disordered and coexistent stable vortex lattices in NbSe_2 single crystals
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• Increase of YBa2Cu3O7 critical currents by Mo substitution and high pressure oxygen annealing
• Pinning of spiral fluxons by giant screw dislocations in YBa_2Cu_3O_7 single crystals: Josephson analog of the fishtail effect