Ultra High Sensitive Niobium NanoSQUID by Focused Ion Beam Sculpting

Abstract

The nanosuperconducting quantum interference device (nanoSQUID) is a powerful tool for nanoscience investigations. In this paper, the main features of niobium nanoSQUID based on deep submicron Josephson tunnel junctions have been investigated. The superconductive nanosensor has a rectangular loop of (1 × 0.4 μm 2) interrupted by two square Josephson junctions having a side length of 0.3 μm. The crucial steps of the fabrication process have been performed using focusing ion beam (FIB) nanosculpting technique. A full characterization of the nanosensor has been performed including the measurement of the voltage swing, the voltage responsivity, the spectral density of the magnetic flux and spin noise and the investigation of the main characteristics as a function of the temperature. Due to a very high responsivity (2.9 mV/ Φ0), the nanodevice exhibited, at T= 4.2 K, an intrinsic spectral density of the magnetic flux as low as 600 n Φ0/Hz 1/2, corresponding to a magnetic moment noise of 9 μB/Hz 1/2. For temperature less than 4.0 K, the nanodevice shows hysteretic current-voltage characteristics. However, the high critical current modulation depths ensure a suitable sensitivity for nanoscale applications.