Temperature dependent pinning phenomenon in superconducting Nb films with triangular and honeycomb pinning arrays

Abstract

The pinning phenomena in superconducting Nb films with triangular and honeycomb pinning arrays were explored. Special temperature dependent phenomena were found for both films. For the film with a triangular pinning array, the pronounced matching peaks in the critical currents as a function of magnetic field reduce from six to three within a narrow temperature range. This temperature dependent matching effect is explained by considering the dramatic change of coherent length with temperature when the temperature is close to T(c). In order to compare with the film with a triangular pinning array, we fabricated a film with a honeycomb pinning array with similar pinning site spacing and pinning size. Special prominent matching peaks at H = 3.5H(1) were found for this film. Molecular dynamic simulations were made to study this phenomenon. The ground state distribution of vortices obtained from simulations reasonably explains the prominent matching peaks. Pronounced temperature dependent matching effects were also found for the film with a honeycomb pinning array.

Vortex interaction enhanced saturation number and caging effect in a superconducting film with a honeycomb array of nanoscale holes

“…Experimental results similar to those observed in our sample B were reported for a superconducting Nb film with a honeycomb array of blind holes with a hole-spacing of 400 nm and a diameter of 270 nm, where the absence of the peak in the critical current at H = 3H 0 was attributed to a special arrangement of vortices in the holes and that the pinning enhancement at H = 3.5H 0 is due to a caging effect 27 . Interestingly, our sample B with through-holes and the Nb films with blind holes have the same estimated saturation number n si = 2 in the experimental temperature ranges.…”

“…For example, extensive molecular dynamics simulations have been conducted in recent years 21 , which revealed remarkable variety of static and dynamic phenomena at integer and noninteger fillings. Experimental studies have also been performed recently, showing unusual features of such superconducting systems such as guided vortex motion [25][26][27][28] . In combination with computer simulations, we reveal that interstitial vortices appear once the saturation number n si predicted for an isolated defect is exceeded.…”

Vortex ratchet reversal at fractional matching fields in kagomélike array with symmetric pinning centers

“…However, in the present case no matching effects are observed beyond H n=1 . This is different from honeycomb arrays 20 in which strong matching effects were experimentally observed up to H = five to six times H n=1 and from kagomé arrays 10 for fields up to two H n=1 and in numerical simulations 21 for fields up to four H n=1 . Actually, matching to the pinning center density has also been observed in triangular lattices of antidots, in which some of the pinning centers had been removed at random, 23 but with a strong suppression of higher order matching upon increasing the fraction of missing pinning sites ͑the second-order matching field was found to disappear in the range 20-40 % of antidot dilution, which is comparable to the 33% fraction of missing dots in the kagomélike array͒.…”

“…The observed matching effects in the kagomélike array are similar to results in other complex lattices such as kagomé and honeycomb [10][11][12][20][21][22] in basic aspects: the main matching fields are also given by pinning center density but matching at noninteger matching conditions is much more relevant than in simple triangular or square arrays due to the diluted geometry. However, in the present case no matching effects are observed beyond H n=1 .…”

Surface Effects on the Dynamic Behavior of Vortices in Type II Superconducting Strips with Periodic and Conformal Pinning Arrays

“…For periodic pinning, such as square [12][13][14][15][16][17][18][19][20][21], triangular [30][31][32][33][34][35]55], honeycomb [27,29,30,38], and Kagomé [27-29, 32, 37], vortices tend to match the pinning lattice in commensurate patterns, which greatly enhances the critical current density. However, these enhancements occur at specific values of magnetic fields, resulting in high oscillations of the critical current as a function of the applied field [13,14,29,[33][34][35][36][37][38][39][40].…”