Vortex deformation and breaking in superconductors: a microscopic description

Abstract

Vortex breaking has traditionally been studied for non-uniform critical current densities, although it may also appear due to non-uniform pinning force distributions. In this article we study the case of a high-pinning/low-pinning/high-pinning layered structure. We have developed an elastic model for describing the deformation of a vortex in these systems in the presence of a uniform transport current density J for any arbitrary orientation of the transport current and the magnetic field. If J is above a certain critical value, J_c , the vortex breaks and a finite effective resistance appears. Our model can be applied to some experimental configurations where vortex breaking naturally exists. This is the case for YBa₂Cu₃O_7−δ (YBCO) low-angle grain boundaries and films on vicinal substrates, where the breaking is experienced by Abrikosov–Josephson vortices (AJV) and Josephson string vortices (SV), respectively. With our model, we have experimentally extracted some intrinsic parameters of the AJV and SV, such as the line tension ϵ _l and compared it to existing predictions based on the vortex structure.

Notes

†Actually, the structure of a vortex in a LAGB for anisotropic superconductors is more complex than the AJV described in 20. The vortex nature in our studied situation is discussed in section 5.1.

†The approximation of κ ≫ 1 produces an error smaller than a 1% for κ ≥ 20.

‡For our experimentally studied situations of Section 5, the condition l_d  ≪ λ _ab is satisfied for ϕ > 5° and θ > 0.5° for LAGB and vicinal films, respectively.

†If the YBCO film is grown on a normal substrate, the transport current flows parallel to the ab planes and there is no breaking phenomenon. For this reason, it is required a miscut angle in the substrate in order to obtain a certain component in the c direction and observe vortex breaking.