Vortex clusters and multiquanta flux lattices in thin films of anisotropic superconductors

Abstract

The distinctive features of equilibrium vortex structures in thin films of anisotropic superconductors in tilted magnetic fields are studied for the limits of moderate and strong anisotropy. The energetically favorable shape of isolated vortex lines is found in the framework of two particular models describing these limiting cases: London theory with an anisotropic mass tensor and London-type model for a stack of Josephson-decoupled superconducting layers. The increase of the field tilting is shown to result in qualitative changes in the vortex-vortex interaction potential: the balance between long-range attractive and repulsive forces occurs to be responsible for a formation of a minimum of the interaction potential vs the intervortex distance. This minimum appears to exist only for a certain restricted range of the vortex tilting angles which shrinks with the decrease of the system anisotropy parameter. Tilted vortices with such unusual interaction potential form clusters with the size depending on the field tilting angle and film thickness or/and can arrange into multiquanta flux lattice. The magnetic flux through the unit cells of the corresponding flux line lattices equals to an integer number M of flux quanta. Thus, the increase in the field tilting should be accompanied by the series of the phase transitions between the vortex lattices with different M .PACS numbers:

Extension of the Ginzburg–Landau approach for ultracold Fermi gases below a critical temperature

“…Recently, the GL method was re-derived in the context of superfluid ultracold Fermi gases [2,3,4,5]. The GL approach was also applied to explain the phenomenon of the "1.5-type" superconductivity.…”

Vortex molecules in thin films of layered superconductors

“…One can observe an interplay between the long-range attractive and the repulsive forces between two zigzag deformed PV stacks, similar to the one between two tilted vortices in layered [8] or anisotropic [10] SC films. Certainly, in a bulk sample (D → ∞) the Pearl term in (18) vanishes, and at long distances the dominant interaction between the zigzag PV lines is an attraction [16].…”

“…When the magnetic field increases, these "molecules" start to build vortex lattice. In fact, the particularity of the intervortex interaction results in the emergence of the flux structures with different number of vortices per unit cell [10].…”

Simulation of the phase diagram of magnetic vortices in two-dimensional superconductors: evidence for vortex chain formation

“…Here, we consider the long-range Pearl repulsion as a candidate [33,34]. It is produced by the stray field near the surface outside the samples and should be important for thin samples [25,35]. Second, the chainlike clustering structure of vortices in superconductors is indicative of intervortex attraction.…”

“…(I-II) For moderately anisotropic superconductors like YB-CO, it has been demonstrated that the field changes sign in some local regions in the plane perpendicular to the flux-line axis under a tilted magnetic field [24][25][26], leading to intervortex attraction in those regions. (IV) For the layered superconductors with very weak inter-layer coupling, the Josephson Vortices (JV) will appear at much lower field near H c1 [25]. The PV are attracted and trapped by JV and thus form chains [27,28].…”