Probing the pinning landscape in type-II superconductors via Campbell penetration depth

Abstract

Type-II superconductors owe their magnetic and transport properties to vortex pinning, the immobilization of flux quanta through material inhomogeneities or defects. Characterizing the potential energy landscape for vortices, the pinning landscape (or short, pinscape), is of great technological importance. Aside from measurement of the critical current density jc and of creep rates S, the ac magnetic response provides valuable information on the pinscape which is different from that obtained through jc or S, with the Campbell penetration depth λC defining a characteristic quantity well accessible in an experiment. Here, we derive a microscopic expression for the Campbell penetration depth λC using strong-pinning theory. Our results explain the dependence of λC on the state preparation of the vortex system and the appearance of hysteretic response. Analyzing different pinning models, metallic or insulating inclusions, as well as δTc and δℓ pinning, we discuss the behavior of the Campbell length for different vortex-state preparations within the phenomenological H−T phase diagram and compare our results with recent experiments.

Source-reported materials — not catalogue approval

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