Vortex matter in intertype superconductivity regime

Abstract

Based on the Ginzburg-Landau (GL) theory, superconducting materials are classified as ideally diamagnetic type-I or type-II, where the magnetic field penetrates the superconducting condensate as a regular lattice of Abrikosov single-quantum vortices, depending on the Ginzburg-Landau parameter κ. However, this simple classification applies only for materials deep in type-I (κ < 1√2) or in deep type-II (κ > 1√2). Superconducting materials with κ in the vicinity of κ₀ ≈ 1√2 reveals non-standard properties that cannot be described within the conventional type-I/type-II dichotomy. These materials are broadly referred as presenting intertype (IT) superconductivity. IT superconductivity appears in a finite interval between types-I and -II amending the standard classification. The existence of the IT superconductivity is a general property of the BCS pairing mechanism and is related to the infinite degeneracy of the Bogomolnyi point. By lowering the temperature or introducing or impurities and/or defects this degeneracy is removed, leading to many unconventional properties of the superconducting mixed state, which are characteristic to the IT superconductivity. The magnetic properties of IT superconductivity cannot be described as a mixture of those in type-I or -II superconductors. In this work we present results on the vortex matter in the IT regime, and discuss the perspective of observing it in films, wires and bilayers superconductors. We use Ginzburg-Landau theory, the Lawrence-Doniach model and Extended Ginzburg Landau formalism to calculate the vortices configurations on these systems. Our calculations reveal exotic flux distribution that are indeed in IT regime, they can be classified into typical patterns which are not found in type-I and type-II superconductors, like: giant vortices and vortex clusters, vortex chains, vortex stripes, superconducting islands separated by vortex chains in the films superconductors. These vortex configurations in IT superconductors depend on the vortex-vortex interaction type. Analysis of the vortex-vortex interactions in the IT domain reveals that they have a considerable many-body (many-vortex) contribution. Such many-body interactions play a crucial role in the formation of the vortex matter in the mixed state, e.g., stabilizing multi-vortex clusters. The properties of the vortex-vortex interactions depend strongly on the number of vortices in a cluster and on the material (κ value). The interaction can be monotonically attractive, monotonically repulsive or, in the major cases, non-monotonic, this being is more noticeable near to the boundary of the IT regime. This observation demonstrates an existence of a special type of vortex matter shaped by many-vortex interactions. Our findings shed a new light on the problem of the interchange between types-I and -II, breaking the grounds of understanding the magnetic response and of superconductors and raise questioning on the completeness of the conventional classification of superconductors materials types.