Direct visualization of vortex pattern transition inZrB12with Ginzburg-Landau parameter close to the dual point

Abstract

In nature, many systems exhibit modulated phases with periodic macroscopic patterns and textures mainly due to the competitive interactions of different phases. Vortex systems in superconductors, which are easy to access, offer the possibility of tuning the ratio between the competitive interactions, providing a unique tool to study the evolution and equilibrium of similar patterns. The κ-T phase diagram of clean superconductors shows the transition from type-I to type-II superconductivity via a narrow κ range near the dual point κ = 1/ √ 2 where the vortices attract each other at long distances and repel each other at short distances. This κ range, which is termed the type-II/1 phase, becomes larger with decreasing temperature. The direct imaging at the scale of individual vortices of the vortex pattern transition would provide valuable information. Therefore, by using scanning Hall probe microscopy, we have performed direct visualization of the vortex pattern transition in a ZrB 12 single crystal across the type-II and type-II/1 phases. By gradually lowering the temperature, and thereby tuning vortex interactions, a transition is observed from the ordered Abrikosov vortex lattice to a disordered vortex pattern with large areas of Meissner phase, vortex chains, and vortex clusters. The formation of vortex chains and clusters has been found to arise from the combined effect of quenched disorder and the attractive vortex-vortex interaction in the type-II/1 phase. The clusters and chains serve as the vortex reservoir to enable the formation of a triangular vortex lattice of the type-II phase at high temperatures.

Stability of degenerate vortex states and multi-quanta confinement effects in a nanostructured superconductor with Kagome lattice of elongated antidots

“…In contrast, one can see a much wider distribution with additional peaks for the disordered vortex state at H a =0.606 mT (point 2, lower panel). As a matter of fact, the similar order-disorder phenomenon has also been observed in other vortex systems [60,61] and it has been recognised that the random environments are usually unaviodable in physical systems.…”

Paramagnetic Meissner effect in ZrB12single crystal with non-monotonic vortex–vortex interactions

“…The step-like jumps are also observed in the M(T) curve when magnetic flux penetrates into the sample under external field (lower inset of figure 2(a)). Due to the relatively weak pinning in our sample [15], the possibility of flux jump in traditional type-II superconductors has also been ruled out. In type-II/1 superconductors, instead of a triangular vortex lattice, vortex clusters form due to the non-monotonic-i.e.…”

“…In this article, as an effort to understand the vortex behavior in a superconductor with non-monotonic vortex interactions, we studied the PME in a high quality ZrB 12 single crystal (2.48 2.48 0.72 mḿ´). The ZrB 12 crystal has a Ginzburg-Landau parameter of 0.8 k » , placing the sample right within the traditional type-I and type-II crossover regime [14,15]. The non-monotonic vortex interactions have also been confirmed by direct visualization of the very inhomogeneous vortex pattern at low temperatures [15].…”

“…The ZrB 12 crystal has a Ginzburg-Landau parameter of 0.8 k » , placing the sample right within the traditional type-I and type-II crossover regime [14,15]. The non-monotonic vortex interactions have also been confirmed by direct visualization of the very inhomogeneous vortex pattern at low temperatures [15]. It was clearly observed that the surface superconductivity of ZrB 12 [16][17][18] favors the formation of PME according to the flux compression mechanism.…”

Vortices in a wedge made of a type-I superconductor

“…As a result, the so-called type-II/1 phase (see e.g. [13][14][15] and references therein), which could be expected when the effective Ginzburg-Landau Λ ξ parameter lies in the close vicinity of 1 2 , appears to be irrelevant: for the wedges under consideration, the width of the corresponding region is comparable to or even smaller than the vortex size.…”