Enhancing the critical current of a superconducting film in a wide range of magnetic fields with a conformal array of nanoscale holes

The maximum current (critical current) a type-II superconductor can transmit without energy loss is limited by the motion of the quantized magnetic flux penetrating into a superconductor. Introducing nanoscale holes into a superconducting film has been long pursued as a promising way to increase the critical current. So far the critical current enhancement was found to be mostly limited to low magnetic fields. Here we experimentally investigate the critical currents of superconducting films with a conformal array of nanoscale holes that have nonuniform density while preserving the local ordering. We find that the conformal array of nanoscale holes provides a more significant critical current enhancement at high magnetic fields. The better performance can be attributed to its arching effect that not only gives rise to the gradient in hole density for pinning vortices with a wide range of densities but also prevents vortex channeling occurring in samples with a regular lattice of holes.

Figure 1

SEM micrographs of sample I. (a) Arrangement of three sections. (b) and (c) Images at higher magnifications for the triangular and conformal arrays, respectively.

Figure 2

Critical currents from sample I. The magnetic field and temperature dependencies of critical currents are presented in (a) and (b), respectively. The inset in (a) shows the zero-field superconducting transitions of the three sections.

Figure 3

Magnetic field dependence of critical currents from sample II and sample III. Sample II (a) and sample III (b) have half the size of holes as those in sample I. Sample III has the same arrangement and diameter but half the depth of the holes as those in sample II. The insets in (b) show the difference in the enhancement of the critical currents induced by through and blind hole arrays in samples II and III; the left and right insets are for the conformal and triangular arrays, respectively.