Fabrication and characterization of high-T_cYBa₂Cu₃O_7−xnanoSQUIDs made by focused ion beam milling

Abstract

We have fabricated high-T(c) nanoscale superconducting quantum interference devices (nanoSQUIDs) with a hole size of 250 nm × 250 nm based on a 100 nm bridge at 77 K by focused ion beam milling and ion implantation. At 78 K, the curve of the voltage branch became roughly linear and agreed with the Josephson-like behavior. The sample exhibited strong flux flow behavior at temperatures under 76 K. The voltage flux characteristic curves, V -I(mod), of the nanoSQUID at different bias currents at 78 K were observed. Typically, critical currents of 15 µA and peak-to-peak values of the voltage flux transfer function of 3.7 µV were measured. The measured data strongly suggest that the weak link structure could be a superconducting metal with a critical temperature T(c)' smaller than that (T(c)) of other YBa(2)Cu(3)O(7-x) (YBCO) films. This fabrication method of combining a nanobridge and ion implantation can improve the yield of nanojunctions and nanoSQUIDs.

Ultra low noise YBa2Cu3O7−δ nano superconducting quantum interference devices implementing nanowires

“…In contrast to previous works [11][12][13] our nanoSQUIDs show critical current modulations as a function of an externally applied magnetic flux in the full temperature range below the transition temperature, T C , of the devices. Both the modulation depth and the period in magnetic field are in good quantitative agreement with numerical computations.…”

“…Several attempts to fabricate HTS nanoSQUIDs, implementing YBCO Dayem bridges, have been made during the last few decades [11][12][13]. However a proper SQUID behavior, with a periodic modulation of the critical current in the full temperature range below T C has never been observed.…”

Non-Gaussian noise effects in the dynamics of a short overdamped Josephson junction

“…Moreover, JJs present a wide range of applications. In particular, in recent years, the JJs have been used to implement both superconducting quantum bits [5][6][7][8] and nanoscale superconducting quantum interference devices for detecting weak magnetic flux changes [9]. Josephson junctions, in fact, represent good candidates to realize solid state superconducting quantum bits (qubits) for quantum information processing.…”

“…For this reason, JJs have been studied at very low temperature in devices making use of charge [10], flux [11] and phase qubits [12]. Moreover, JJs are widely used for their high sensitivity to magnetic flux changes [9].…”

Flux-coherent series SQUID array magnetometers operating above 77 K with superior white flux noise than single-SQUIDs at 4.2 K

“…[3][4][5] Also, significant is the progress reported in the area of nanofabrication. [6][7][8] At present, however, due to their superior flux noise performances in the vast majority of applications, SQUIDs made of low temperature superconductors (LTS) and operating at 4.2 K are being used. This is despite several significant advantages HTS SQUIDs operating above 77 K offer: low cost and user-friendly cooling procedures (at a time, when the price of liquid He is increasing significantly) and potential superiority as magnetic imaging devices due to a reduced separation between the sensors and the room temperature object under study (because of the decreased thermal insulation demand).…”