Abstract
We demonstrate theoretically and experimentally the generation of rectified mean vortex displacement resulting from a controlled difference between the surface barriers at the opposite borders of a superconducting strip. Our investigation focuses on Al superconducting strips where, in one of the two sample borders, a saw tooth-like array of micro-indentations has been imprinted. The origin of the vortex ratchet effect is based on the fact that (i) the onset of vortex motion is mainly governed by the entrance/nucleation of vortices and (ii) the current lines bunching produced by the indentations facilitates the entrance/nucleation of vortices. Only for one current direction the indentations are positioned at the side of vortex entry and the onset of the resistive regime is lowered compared to the opposite current direction. This investigation points to the relevance of ubiquitous border effects typically neglected when interpreting vortex ratchet measurements on samples with arrays of local asymmetric pinning sites.
Highlights
We demonstrate theoretically and experimentally the generation of rectified mean vortex displacement resulting from a controlled difference between the surface barriers at the opposite borders of a superconducting strip
New Journal of Physics 15 (2013) 063022 1367-2630/13/063022+13$33.00. This surface barrier, inherently present in finite superconducting samples, is not symmetric, i.e. the energy needed to introduce a vortex into the sample is different from that needed to remove the vortex from the sample. This difference between vortex nucleation and vortex exit leads to metastabilities that manifest themselves as hysteretic magnetization curves [19, 20]
Only for one particular current direction the barrier for vortex entry is drastically reduced, which is manifested in a clear difference between the measured dissipation for both current directions
Summary
We demonstrate theoretically and experimentally the generation of rectified mean vortex displacement resulting from a controlled difference between the surface barriers at the opposite borders of a superconducting strip. For one current direction the indentations are positioned at the side of vortex entry and the onset of the resistive regime is lowered compared to the opposite current direction This investigation points to the relevance of ubiquitous border effects typically neglected when interpreting vortex ratchet measurements on samples with arrays of local asymmetric pinning sites. This surface barrier, inherently present in finite superconducting samples, is not symmetric, i.e. the energy needed to introduce a vortex into the sample is different from that needed to remove the vortex from the sample. The experimental findings are in agreement with time-dependent Ginzburg–Landau (TDGL) simulations
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