Complex dynamical flow phases and pinning in superconductors with rectangular pinning arrays

Abstract

We examine vortex pinning and dynamics in thin-film superconductors interacting with square and rectangular pinning arrays for varied vortex densities including densities significantly larger than the pinning density. For both square and rectangular pinning arrays, the critical depinning force shows maxima at only certain integer matching fields where the vortices can form highly ordered arrays. For rectangular arrays the depinning force and commensurability effects are anisotropic with a much lower depinning threshold for vortex motion in the easy flow directions. We find evidence for a crossover in pinning behavior in rectangular pinning arrays as the field is increased. We also show analytically, and confirm with simulations, that for B = 2B φ the strongest pinning can be achieved for rectangular pinning arrangements rather than square for one direction of driving force. Under an applied driving force we find a remarkable variety of distinct complex flow phases in both square and rectangular arrays. These flow phases include stable sinusoidal and intricate pinched patterns where vortices from different channels do not mix. As a function of the driving force certain flow states become unstable and transitions between different phases are observed which coincide with changes in the net vortex velocities. In the rectangular arrays the types of flow depend on the direction of drive. We also show that two general types of plastic flow occur: stable flows, where vortices always flow along the same paths, and unstable or chaotic flows.

Dynamic regimes for driven colloidal particles on a periodic substrate at commensurate and incommensurate fillings

“…Under an applied drive, a number of incommensuration and soliton vortex flow states were observed at fillings a few percent above and below f = 1.0 [8]. Simulations at high fillings in these vortex systems produced a variety of dynamical phases [55]; however, experimental observations of these regimes have proven difficult, in part due to the possibility of multiply occupied pinning sites. Since the vortices have no hard core, they can merge to form multiquantized vortex states trapped at the pinning sites.…”

Vortex configurations and critical parameters in superconducting thin films containing antidot arrays: Nonlinear Ginzburg-Landau theory

“…In this regime, the vortices act like charged point particles and their interaction with periodic pinning potential can be described using molecular dynamic simulations. 18,19,20,21 . However, the overlap of vortex cores (with size ∼ ξ), and the exact shape of the inter-vortex interaction (depending on the superconducting material properties reflected through κ), may significantly modify the vortex structures and consequently the critical current when this criteria is no longer satisfied.…”

“…In this respect, arrays of microholes (antidots) 1,2,3,4,5,6,7,8,9,10,11,12 and submicron magnetic dots, 13,14,15 have been studied, as their presence in the SC film strongly modifies the vortex structure compared to the one in non-patterned films. 16,17 Direct imaging experiments, 1 magnetization and transport measurements, 2,3,4,5 and theoretical simulations 18,19,20,21,22 of vortex structures in samples with periodic pinning centers have shown that the vortices form highly ordered configurations at integer H n = nΦ 0 /S and at some fractional H p/q = p q Φ 0 /S (n,p,q being integers) matching fields, where Φ 0 = hc/2e = 2.07 · 10 −7 Gcm 2 is the flux quantum, and S is the area of the primitive cell of the artificial lattice. This remarkable variety of stabilized vortex lattices may even be broadened by multiple possible degeneracies.…”

“…For example, extensive molecular dynamics simulations 18,19,20,21,22 in the London limit have been performed in an attempt to calculate the vortex structure and their dynamics in a periodic pinning potential. Although the general behavior of vortex lattices was accurately described, made approximations are valid only in certain range of parameters.…”

The Effects of Pinning on Critical Currents of Superconducting Films

“…By using lithography it is possible to create well-defined periodic nanostructured arrays with well-defined periodic pinning structures in which the microscopic pinning parameters, such as size, depth, periodicity, and density, can be carefully controlled. This enhancement of critical currents using periodic arrays has recently been demonstrated for high T c superconductors [1][2][3][4][5][6][7][8][9][10][11]. Therefore, the study of pinning mechanisms and vortex motion, from both the experimental and theoretical point of view, it is important to understand and to create materials with more applicability.…”