Flux-line lattices in artificially layered superconductors

Abstract

The flux line lattice of superconductors has been investigated when there exists a periodicity in the underlying system, such as can occur in artificially layered structures. For small fields parallel to the layers the flux lines enter the sample in sequential rows, with the possibility of jumps in the magnetization as new rows are created. As the field is increased these discontinuities gradually decrease, but there still exist transitions between states that are aligned differently to the periodic direction. Increasing the magnitude of the periodic potential reduces the competition between differently aligned lattices and tends to lock in one particular alignment. The effect of transitions on the shear modulus is also discussed and related to the experiments of Theunissen et al.

Josephson-Vortex-Glass Transition in Strong Fields

“…We emphasize that this conclusion is independent of the strength of the point disorder and of the strength B of the magnetic field which tunes the structure of the disorder-free vortex solid in B ⊥ c through a commesurability condition 5,29,18) with the layer structure. Namely, the glass phase in the model (3.7) should have the anisotropic TME irrespective of B.…”

“…In §2, the model (1.2) with the term (1.3) is examined consistently with ref.5 using the LLL approximation, and the glass susceptibility χ G (k) is examined to find a glass transition line of the Josephson vortex system, i.e., of B ⊥ c case of the LD model by focusing on the nontrivial high field regime B > φ 0 /(2πd 2 √ Γ). In §3, it is demonstrated by examining tilt responses of the LD model and of the closely related uniaxially periodic model 18) that the resulting Josephson-vortex-glass (JG) phase should have a transverse Meissner effect (TME) for a tilt perpendicular to the layers, while the response for a tilt within the layers (perpendicular to c axis) remains nonsuperconducting.…”

“…To clarify these points, we examine the tilt responses in the uniaxially periodic GL model 18) with point disorder…”