Anisotropic vortex pinning in superconductors with a square array of rectangular submicron holes

Abstract

We investigate vortex pinning in thin superconducting films with a square array of rectangular submicron holes ("antidots"). Two types of antidots are considered: antidots fully perforating the superconducting film, and "blind antidots", holes that perforate the film only up to a certain depth. In both systems, we observe a distinct anisotropy in the pinning properties, reflected in the critical current Ic, depending on the direction of the applied electrical current: parallel to the long side of the antidots or perpendicular to it. Although the mechanism responsible for the effect is very different in the two systems, they both show a higher critical current and a sharper IV-transition when the current is applied along the long side of the rectangular antidots.

Guided vortex motion in superconductors with a square antidot array

“…9,10 In a superconductor with a random distribution of pinning centers, an isotropic vortex mobility is expected with a vortex motion parallel to the Lorentz force. On the other hand, if the rotational symmetry of the pinning potential is broken, the response will be anisotropic, 11 and guided vortex motion may appear.…”

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

“…It is now well established that these artificial pinning centers (i) hold great potential for enhancing the critical parameters of the sample and (ii) give rise to different kinds of vortex behavior that is not observed in the presence of random pinning. 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.…”

Experimental determination of the number of flux lines trapped by microholes in superconducting samples

“…As it has been demonstrated in previous theoretical 22 and experimental studies, [10][11][12] rearrangements of the vortex lattice at the matching fields nH 1 have a profound effect on the critical current. Accordingly, these changes in the pinning properties of the flux line lattice should be also reflected in changes of the efficiency to screen out a perturbative external ac field.…”

“…[10][11][12] These maxima in the screening are accompanied by local dips in the dissipation. Interestingly, at 6H 1 the screening undergoes a dramatic reduction, which coincides with the maximum dissipation.…”

“…For H Ͼ n s H 1 , commensurability effects between the interstitial vortex configuration and the pinning array give rise to local increments of the critical current J c . [10][11][12] Although these effects have been mainly studied by transport and dc magnetization measurements, less explored has been the ac response of these systems. 11,13-15 ac susceptibility allows one to readily cover a wide range of dynamic regimes from a passive linear regime, preserving the initial vortex configuration, to the highly disturbing critical state regime, by simply sweeping the amplitude h of the ac drive.…”