Abstract
We present a comparative study of vortex pinning efficiency in superconducting (V) thin films grown on two similar triangular arrays of superconducting (Nb) and nonsuperconducting (Cu) nanodots. Resistance and magnetization anomalies at the same matching fields confirm the same pinning periodicity in both samples. However, we found two distinct features: First, the sample with superconducting dots shows stronger pinning that appears as sharper matching peaks in magnetization loops and shows higher critical current density and larger critical field at low temperatures. Second, an overall increase in the resistance of the V film with Nb nanodots is observed, while there is a crossover in the temperature dependence of the critical field and the critical current of both samples at T=3K. This crossover corresponds to the temperature when the superconducting coherence length of V thin film equals the edge-to-edge distance between nanodots. We argue that this change in superconducting properties is related to the change in the superconducting regime from pinning enhancement at low temperatures to a superconducting wire network at high temperatures.
Highlights
The improvement of vortex pinning efficiency in type-II superconductors has been the focus of many experimental and theoretical investigations [1]
This crossover corresponds to the temperature when the superconducting coherence length of V thin film equals the edge-to-edge distance between nanodots. We argue that this change in superconducting properties is related to the change in the superconducting regime from pinning enhancement at low temperatures to a superconducting wire network at high temperatures
These matching effects are due to the additional suppression of the SC critical temperature (TC) by magnetic field at noninteger flux quantum values arising from the fluxoid quantization, the so-called Little-Parks effect [16,17]
Summary
The improvement of vortex pinning efficiency in type-II superconductors has been the focus of many experimental and theoretical investigations [1]. It is well established that artificial pinning centers can substantially enhance the superconducting critical current density (JC) whenever the density of vortices matches the underlying pinning landscape (“pinning enhancement”) This commensurability effect between vortices and pinning landscape has been widely studied in different periodic [2] and nonperiodic [3,4] pinning geometries using pinning centers such as micrometric and submicrometric holes [5,6,7,8], blind holes [9,10], and magnetic [11,12] and nonmagnetic dots [13,14]. When the width (w) of the superconducting (SC) strips around the dots is comparable to the SC coherence length, ξ (T ), the vortices are too large to locate in interstitial positions In this case, matching occurs at integer flux quantum fields, but the sample is described as a SC wire network [15]. These matching effects are due to the additional suppression of the SC critical temperature (TC) by magnetic field at noninteger flux quantum values arising from the fluxoid quantization, the so-called Little-Parks effect [16,17]
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