NANO-SQUIDs based on niobium Dayem bridges for nanoscale applications

Abstract

Abstract. We report on the design, the fabrication and the performance of an integrated magnetic nano-sensor based on niobium dc-SQUID (Superconducting QUantum Interference Device) for nanoscale applications is presented. The nano-sensors are based on nanometric niobium constrictions (Dayem bridges) inserted in a square loop having a side length of 200 nm. Measurements of voltage-flux characteristic, flux to voltage transfer factor and noise performances are reported. In small signal mode, the sensors have shown a magnetic flux noise spectral density of 1.5 µΦ 0 /Hz 1/2 corresponding to a spin sensitivity in unit of Bohr magneton of 60 spin/Hz 1/2 . Supercurrent decay measurements of these devices are also reported. Such measurements provide useful information for applications which employ the SQUID as a trigger where the sensor works on the zero voltage state. The experimental data, have shown an intrinsic current fluctuation less than 0.2% of the critical current at liquid helium temperature, corresponding to an intrinsic sensor magnetic flux resolution of a few mΦ 0 . In view of the nano-SQUID employments in the detection of small spin populations, the authors calculated the spin sensitivity and the magnetic response relative to the single spin, as a function of its position within the SQUID hole. The results show that the SQUID response depends strongly on the spin position.

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.…”

“…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 e 4 1 ( ) -/ were reported in Al-based ring-shaped devices 8,31,32) where the lateral size is comparable to x of Al. According to Refs.…”