Crossover from intravalley to intervalley vortex motion in type-II superconductors with a periodic pinning array

Abstract

We have determined the transition from intravalley vortex motion ͑Campbell regime͒ to intervalley motion ͑critical state regime͒ in Pb thin films with and without a square array of holes ͑antidots͒ by means of ac susceptibility ͑T , H͒ measurements. The Campbell regime is characterized by a maximum dissipation max Љ dependent on the ac excitation h but nearly temperature independent. In contrast, in the critical state regime, the height of the dissipation peak remains constant, whereas its position shifts to lower temperatures with increasing h. We introduce an alternative way for determining the temperature dependence of the ac onset of the Bean critical state by analyzing the critical current density J͑T͒ extracted from the Ј͑T͒ data at several h. We demonstrate that the presence of a periodic pinning array strongly affects the extension of the crossover area in the h − T diagram between these regimes. We show that this effect can be ascribed to the lower dispersion of the pinning energy together with the higher topological order for the antidot sample.

Microscopic picture of the critical state in a superconductor with a periodic array of antidots

“…The superconductor-to-normal transition at zero field occurs at T c = 7.2 K. More details concerning the sample preparation can be found in Ref. 10.…”

Observation of commensurability effects in a patterned thin superconducting Pb film using microwave reflection spectrometry

“…Among these well-ordered constructions much interest is generated by arrays of completely etched holes (the so-called antidots), with sizes much larger than the superconducting coherence length ξ , which have been demonstrated to trap magnetic flux very * jcuadra@ubxlab.com † agarciasan@ub.edu effectively [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. The interaction of the vortex lattice with such a regular array close to the superconducting transition temperature T c results in a wide range of commensurability effects at low magnetic fields, for integer or fractional numbers of flux quanta per pinning site.…”

Probing the low-frequency vortex dynamics in a nanostructured superconducting strip

“…Additional depletion can also be attributed to the long range nature of the screening current. 47,48 However, the experimental observation in antidot systems of pronounced matching effects at values of the applied field that coincide with the expected flux-density, µ 0 H = nB 1 , [10][11][12][13][14][15][16][17][18][19][20][21][22] suggests that the depletion zone is much narrower than the sample itself. In any case, as shown in the Supplemental Material, our results do not depend strongly on the width of the fluxdepleted region.…”

“…We performed the fitting for both temperatures using the zero temperature penetration depth, λ(0), and the probe height, z 0 [appearing in Eq. (9) (17)- (20). These values were obtained by fitting the model (lines) to the experimental data (symbols) corresponding to averaging the in-phase (e) and the out-of-phase (f) SSM images over the scan area.…”

“…[10][11][12] This reflects in different (according to whether or not interstitial vortices are present) scenarios of the sample response to an excitation, as indeed observed in a great deal of macroscopic ac-susceptibility experiments. [13][14][15][16][17][18][19][20][21][22] The interpretation of the different dynamical regimes usually ig-nores the random pinning potential produced by sample inhomogeneities, considered negligible at the temperatures where the experiments are carried out. However, at least for experiments performed within the linear regime, where vortices are driven close to their equilibrium positions by very small driving forces, the weak material pinning might become important or even dominant.…”