Current-induced SQUID behavior of superconducting Nb nano-rings


  Omri J. Sharon [1]  ,  Avner Shaulov [1]  ,  Jorge Berger [2]  ,  Amos Sharoni [1]  ,  Yosi Yeshurun [1]  
[1] Department of Physics and Institute of Nano Technology, Bar-Ilan University, 5290002 Ramat-Gan, Israel
[2] Department of Physics and Optical Engineering, Ort Braude College, 21982 Karmiel, Israel

The critical temperature in a superconducting ring changes periodically with the magnetic flux threading it, giving rise to the well-known Little-Parks magnetoresistance oscillations. Periodic changes of the critical current in a superconducting quantum interference device (SQUID), consisting of two Josephson junctions in a ring, lead to a different type of magnetoresistance oscillations utilized in detecting extremely small changes in magnetic fields. Here we demonstrate current-induced switching between Little-Parks and SQUID magnetoresistance oscillations in a superconducting nano-ring without Josephson junctions [1]. Our measurements in Nb nano-rings show that as the bias current increases, the parabolic Little-Parks magnetoresistance oscillations become sinusoidal and eventually transform into oscillations typical of a SQUID. We associate this phenomenon with the flux-induced non-uniformity of the order parameter along a superconducting nano-ring, arising from the superconducting leads ('arms') attached to it. Current enhanced phase slip rates at the points with minimal order parameter create effective Josephson junctions in the ring, switching it into a SQUID.

 

[1] Omri J. Sharon, Avner Shaulov, Jorge Berger, Amos Sharoni, and Yosi Yeshurun, Current-induced SQUID behavior of superconducting Nb nano-rings, Scientific Reports 6, 28320 (2016).