European Dissemination of the Ultra-low Temperature Scale, PLTS-2000

Following the introduction of the provisional low-temperature scale from 0.9 mK to 1K, PLTS-2000, there is a need for primary and secondary thermometers and fixed points, which can disseminate the scale to users. This paper reports on the progress, within the EU collaborative project ‘ULT Dissemination’, in the development and evaluation of several devices with associated instrumentation. Principal among them are a current-sensing noise thermometer, a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second-sound thermometer, a 3He melting pressure thermometer for a direct realisation of the PLTS-2000. A superconductive reference device has also been developed, as a replacement for the NBS SRM-768 which is no longer available

A 19-channel d.c. SQUID magnetometer system for brain research

A 19-channel d.c. SQUID magnetometer system for neuromagnetic investigations is under constuction. The first-order gradiometers for sensing the signal are placed in a hexagonal configuration. D.c. SQUIDs based on niobium/aluminium technology have been developed, leading to a field sensitivity of about 5 fT/ Hz. SQUID read-out is realized with a resonant transformer circuit at 100 kHz. The multichannel control and detection electronics are compactly built

Superconducting Quantum Interference Device based on MgB2 nanobridges

The recently discovered superconductor MgB2, 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 MgB2 thin films. Modulation voltages of up to 30 microvolt are observed in an all-MgB2 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/cm2 at 4.2 K.Comment: submitted to Appl. Phys. Let

The road to magnesium-diboride thin films, Josephson junctions and SQUIDs

The remarkably high critical temperature at which magnesium diboride (MgB2) undergoes transition to the superconducting state, Tc approx 40 K, has aroused great interest and has encouraged many groups to explore the properties and application potential of this novel superconductor. For many electronic applications and further basic studies, the availability of superconducting thin films is of great importance. Several groups have succeeded in fabricating superconducting MgB2 films. An overview of the deposition techniques for MgB2 thin film growth will be given, with a special focus on the in situ two-step process