Current-induced SQUID behavior of superconducting Nb nano-rings

Abstract

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. 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.

Toward the Light‐Operated Superconducting Devices: Circularly Polarized Radiation Manipulates the Current‐Carrying States in Superconducting Rings

“…Modern technologies make it possible to fabricate Nb nano-rings with a width and thickness ≈ 30 − 50 nm, a radius R as small as 300 nm and 𝜆 ≈ 𝜉 ≈ 100 nm. [40] These characteristics correspond to the parameters used in our model and 10% deviation of the external flux from Φ 0 ∕2 can be tolerated (see Figure 4). The magnetic field generated by the superconducting current at the center of the nano-ring is of the order of B(0) ≈ 10 −3 − 10 −4 T. This field amplitude can be easily detected by magnetometer based on scanning of a nano-SQUID [41,42] or nitrogen vacancy centers in a diamond tip.…”

Higher harmonic resistance oscillations in micro-bridge superconducting Nb ring

“…We tried to see resistance oscillations with higher harmonic terms even in the simple ring device by tuning the measurement current and also by using several different ring devices, but such higher harmonic oscillations have never been observed. In addition, to the best of our knowledge, higher harmonic components have not been reported in previous superconducting Nb ring devices [25][26][27][28][29][30] Harmonic oscillations with a frequency of (ℎ 4𝑒 ⁄ ) −1 were reported in Al-based ring-shaped devices 8,31,32) where the lateral size is comparable to 𝜉 of Al. According to Refs.…”

Asymmetric nanowire SQUID: Linear current-phase relation, stochastic switching, and symmetries

“…Superconducting quantum interference devices [1,2] (SQUIDs) are known to be extremely sensitive to weak magnetic fields, and therefore various forms of superconducting loops have recently attracted significant attention [3][4][5][6][7][8][9][10][11]. Nanowire networks [12] and loops [13][14][15][16][17][18][19][20] are qualitatively distinct from conventional Josephson junction and SQUIDS due to the linear nature of the nanowire CPR [13].…”