Enhanced vortex pinning by a composite antidot lattice in a superconducting Pb film

Abstract

The use of artificial defects is known to enhance the superconducting critical parameters of thin films. In the case of conventional superconductors, regular arrays of submicron holes ͑antidots͒ substantially increase the critical temperature T c ͑H͒ and critical current I c ͑H͒ for all fields. Using electrical transport measurements, we study the effect of placing an additional small antidot in the unit cell of the array. This composite antidot lattice consists of two interpenetrating antidot square arrays with a different antidot size and the same lattice period. The smaller antidots are located at the centers of the cells of the large antidots array. We show that the composite antidot lattice can trap a higher number of flux quanta per unit cell inside the antidots compared to a reference antidot film without the additional small antidots. As a consequence, the field range in which an enhanced critical current is observed is considerably expanded. Finally, the possible stable vortex lattice patterns at several matching fields are determined by molecular-dynamics simulations.

Enhanced pinning and proliferation of matching effects in a superconducting film with a Penrose array of magnetic dots

“…In both limits clear aperiodic commensurability effects are identified and associated with different stable vortex configurations. The proliferation of matching peaks associated with the local symmetry of the underlying pinning array gives rise to a wide field range of enhanced critical current somehow similar to that observed in composite array of microholes [12]. …”

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

“…6(b) in Ref. 9 demonstrates a clear overshoot of the critical current at H = H 3 with respect to the one at H = H 2 , at the temperature 0.974T c0 . Fig.…”

“…This effect that the critical current is larger for larger fields was recently observed experimentally. 9 The considered sample was a Pb film of thickness 50nm, with square antidots of size a = 0.5µm and period W = 1.5µm. The coherence length and the penetration depth at zero temperature were estimated to be ξ 0 = 40nm and λ 0 = 80nm.…”

“…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.…”

Vortex kinks in superconducting films with periodically modulated thickness

“…The typical matching signature is the appearance of minima in the resistivity (or maxima in the critical current) for magnetic fields such that the number of vortices n V is a multiple (or a simple fraction like 1/4, 1/2 and 3/4) of the number of minima n P in potential landscape. For this purpose, films having different types of artificial pinning centers like holes [1,2] magnetic [3,4] or non-magnetic particles [5] in different geometries [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21], have been studied both experimentally and theoretically [22,23,24,25,26,27,28,29,30].…”