Dynamic vortex phases and pinning in superconductors with twin boundaries

Abstract

We investigate the pinning and driven dynamics of vortices interacting with twin boundaries using large scale molecular dynamics simulations on samples with near one million pinning sites. For low applied driving forces, the vortex lattice orients itself parallel to the twin boundary and we observe the creation of a flux gradient and vortex free region near the edges of the twin boundary. For increasing drive, we find evidence for several distinct dynamical flow phases which we characterize by the density of defects in the vortex lattice, the microscopic vortex flow patterns, and orientation of the vortex lattice.We show that these different dynamical phases can be directly related to microscopically measurable voltage-current V (I) curves and voltage noise. By conducting a series of simulations for various twin boundary parameters we derive several vortex dynamic phase diagrams.

Critical currents, pinning forces and irreversibility fields in (YxTm1−x)Ba2Cu3O7 single crystals with columnar defects in fields up to 50 T

“…Once the applied field exceeds B φ• , interstitial flux lines, which are more mobile [8,9], give rise to a monotonously decreasing j c,m . This was recently observed [8] and also confirmed by flux-gradient driven molecular dynamics simulations of interacting vortices on a random distribution of defects [34] . Not only the change in j c,m by adding columnar defects can be accounted for, also the observed shift of the irreversibility line can be explained by turning to an effective matching field B φ• which itself is dependent upon the applied magnetic field.…”

Orientational ordering, buckling, and dynamic transitions for vortices interacting with a periodic quasi-one-dimensional substrate

“…Previous studies of vortices driven at varied angles through 2D periodic pinning arrays show that the substrate can induce a number of dynamical effects, including directional locking of the vortex motion as well as vortex channeling effects 67,[99][100][101][102] . For a q1D substrate, vortices driven at arbitrary angles should exhibit channeling along the substrate troughs, and the drive at which this channeling is overcome and the vortices start to flow in the direction of drive should be a function of driving angle.…”

Simulation and experiment of vortex transport properties in a Type II superconductor with grain boundary

“…[1], we consider a two-dimensional (2D) slice in the x-y rectangular system (see Figure 1) of an infinite 3D sample with a magnetic field vertical to the slab plane, where we take the vortices in the sample as pillars and use periodic boundary conditions for the x-axis and y-axis directions [1][2][3][4][5][6][7][8][9][10][11][12][13]. These stiff flux lines could be regarded as representing the "center of mass" locations of real, somewhat flexible vortices, and the pinning in the bulk as representing the average of the pinning along the length of the real vortex [1]. The ith vortex motion can be numerically addressed by the overdamped equation [7,8] as follows:…”

“…Vortex transport properties which play an increasingly crucial role in the research of high-temperature superconductors have developed into fascinating fields both theoretically and experimentally [1][2][3][4][5][6][7][8][9][10][11][12]. Numerous defects including dislocations, oxygen-vacancy clusters, second phases, flux inclusions, twin boundaries and irradiation-caused defects are found to be pinning sites for vortex motion against the Lorentz force arising from external current in high-T c superconductors [13].…”