Origin of the critical-current deviation near the critical field

Determine the origin of the deviation of the forward critical current, I_c^+, from its theoretical value near the critical field H_c in Sn10-Pb90 coil-shaped superconducting diodes, including whether the deviation arises from small misalignments of the external-field direction or from variations in coil structure such as wire diameter or shape.

Background

The coil-shaped superconducting diode concept predicts that the forward critical current I_c^+ should increase with external magnetic field because the field generated by the coil partially compensates the applied field. Measurements on the improved Sn10-Pb90 coil diodes showed that I_c^+ increases up to approximately 400 Oe but then rises more slowly than the idealized theoretical prediction at higher fields. This deviation limits realization of the theoretically expected rectification performance near the critical field H_c.

The authors explicitly state that their experiments do not resolve the cause of this discrepancy. They suggest that I_c^+ may be sensitive to small deviations in the external-field direction or to structural parameters of the coil, including wire diameter and shape, identifying these factors as subjects for further investigation and design optimization.