Dynamic regimes in films with a periodic array of antidots

Abstract

We have studied the dynamic response of Pb thin films with a square array of antidots by means of ac susceptibility χ(T, H) measurements. At low enough ac drive amplitudes h, vortices moving inside the pinning potential give rise to a frequency-and h-independent response together with a scarce dissipation. For higher amplitudes, the average distance travelled by vortices surpasses the pinning range and a critical state develops. We found that the boundary h * (H, T ) between these regimes smoothly decreases as T increases whereas a step-like behavior is observed as a function of field. We demonstrate that these steps in h * (H) arise from sharp changes in the pinning strength corresponding to different vortex configurations. For a wide set of data at several fields and temperatures in the critical state regime, we show that the scaling laws based on the simple Bean model are satisfied.

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.…”

“…[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.…”

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

“…22 Most of this research has been done in conventional (low T c ) superconductors where the ac response is weakly dependent on the excitation frequency (up to 10 kHz), indicating that vortex relaxation processes are not relevant. 23 This frequencyindependent ac response allows us to directly visualize the vortex response under very slowly (∼2 mHz) varying fields. The results of these measurements, obtained at T = 7 K and with an ac amplitude of 1 Oe > H * , are summarized in Fig.…”

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

“…Different regimes of vortex dynamics have been investigated by varying either the ac perturbation sensing parameters (drive amplitude H ac , and frequency f ac ) or the thermodynamic variables (dc magnetic field H dc and temperature T ) [18,19,[21][22][23]43,44]. These low-H ac measurements in the kilohertz frequency range have been proven successful and sensitive to investigate the effective pinning potential without modifying the vortex distribution, facilitating a direct correlation between the vortex lattice configuration and the observed dynamical response.…”