Critical current and persistent supercurrent in asymmetric superconducting rings

Magnetic flux quantization through superconducting rings dictate that they contain a persistent supercurrent which switches direction at half-integer external flux quanta. The oscillatory persistent supercurrent manifests in critical current and resistance (Little–Parks) oscillations. Recently, it was shown theoretically and experimentally [1] that in an asymmetrically connected superconducting ring, the critical current may exhibit anomalous periodic behavior with external magnetic flux, including discontinuous jumps. Significant inconsistencies exist between experimental and simulation results [1]. We have performed modeling of the critical current in a superconducting ring as a function of geometrical asymmetries. Our simulations indicate that persistent current might not switch direction at the most energetically favorable locations; and the geometric asymmetry could be used to control the switching. Experimentally, asymmetric superconducting rings have been fabricated by electron-beam lithography, and the critical current will be measured and compared with the simulations. The results may find implications in novel superconducting electronics relying on flux quantization such as superconducting qubits and nano SQUIDs.
[1] A.A. Butrlakov, et al., JETP Lett. 99, 169 (2014).