Superconducting quantum interference devices (SQUIDs) based on niobium nanobridges have been produced by means of focused ion beam milling. Typical critical currents of 4−25 μA and flux sensitivities of 40−200 μV/Φ0 were measured for sensors based on 80 nm wide, 50 nm thick, and 150 nm long bridges. A white flux noise level of 1.5 μΦ0/Hz1/2 was measured for a device with an area of 900 μm2 and a critical current of 15 μA. The effective area of the smallest produced SQUID was 3.6 × 10-2 μm2. Possible applications for such miniature SQUIDs are in scanning SQUID microscopy and the study of magnetic nanoparticles.

The recently discovered superconductor MgB 2 , with a transition temperature of 39K, has significant potential for future electronics. An essential step is the achievement of Josephson circuits, of which the superconducting quantum interference device (SQUID) is the most important. Here, we report Josephson quantum interference in superconducting MgB 2 thin films. Modulation voltages of up to 30 µ µ µ µV are observed in an all-MgB 2 SQUID, based on focused ion beam patterned nanobridges. These bridges, with a length scale < 100 nm, have outstanding critical current densities of 7 x 10 6 A/cm 2 at 4.2 K.

Superconducting quantum interference devices ͑SQUIDs͒ and magnetometers are fabricated from nanoconstrictions in epitaxial MgB 2 films. The nanobridges are contained within single-crystalline grains, resulting in clean transport, a large critical current density of 5 ϫ 10 7 A/cm 2 at 4.2 K, and stable SQUID voltage modulation up to 38.8 K. The magnetometer is realized with an inductively coupled pickup loop, giving rise to a field sensitivity of 1 pT Hz −1/2 down to 1 Hz. The device properties are governed by the two-band superconducting nature of MgB 2 , posing, however, no problems to a successful development of boride magnetic field sensing devices. The MgB 2 zero-temperature London penetration depth is measured to be 62 nm, close to theoretical predictions.

Abstract-A quantitative knowledge of inter-filament transverse resistance will allow us to describe current redistribution processes inside strands more accurately. This is particularly important for the analysis of the influence of strain and crack distribution patterns in Nb 3 Sn filaments on the shape of the voltage-current curves. Several indirect methods are commonly used to assess inter-filament resistance. Here we use a direct method to measure transverse inter-filament resistance and filament-to-matrix contact resistance. Two four-probe voltage-current methods are developed for measurements below 10 K at various background magnetic fields. In addition to FEM (Finite Element Method) simulation, also a new 3D strand model is developed to simulate the current-and voltage distributions. The experimental methods, first results as well as the simulations using the FEM method and new 3D strand model are described.Index Terms-Current distribution, inter-filament resistance, NbTi, Nb 3 Sn, proximity effect, 3D strand model.

YBa,Cu,O, nano-bridges with widths ranging from 200 to 800nm were made using Focused Ion Beam milling. The IV-characteristics of the narrowest nano-bridges show, under microwave irradiation, pronounced Shapiro steps up to the transition temperature. An inductively shunted single layer SQUID, using these nano-bridges, has been realised by a combination of Focused Ion Beam milling and selective epitaxial growth. Flux to voltage modulation up to 82K was observed, with a maximum modulation depth of 3.7 pV at 78K.