Temperature dependence of the pinning potential in YBa2Cu3O7−x superconductors

Abstract

Voltage-current curves obtained from transport measurements on c-axis-oriented thin films of YBa2Cu3O7−x allow us to determine the temperature, field, and field-orientation dependence of the pinning potential on the basis of the simple Kim-Anderson model for the thermal activation of flux lines. A strong increase of the pinning potential is found at low temperatures, followed by a field-dependent maximum between 60 and 70 K and a decrease towards the transition temperature Tc. The results are compared to literature data of the pinning potential U0(T) obtained from relaxation measurements and discussed in terms of thermal activation theory and related models for the current dependence of U0. The analysis of the E-J curves, results on the angular dependence of Jcab, calculations of the pinning potential based on the core contribution, and due consideration of the different nature of the flux lines at low and high temperatures lead to a consistent picture, in which all results are explained in a qualitative way, without the need of invoking recent models on complex pinning interactions and on new phases of the flux-line lattice. It is shown that the pinning potential at low temperatures is of the order of the core contribution of a small number of pancake vortices and therefore intrinsically limited to small values, while at higher temperatures the correlation length along the field direction increases, which naturally leads to higher potentials.

Source-reported materials — not catalogue approval

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