Integrated Superconducting Submillimeter-Wave Receivers

We overview recent achievements in the field of cryogenic submillimeter-wave receivers based on superconductor–insulator–superconductor (SIS) tunnel junctions. The main attention is paid to the novel superconducting integrated receivers (SIRs) with an on-chip superconducting local oscillator. The single-chip microcircuit of the receiver, which integrates a quantum mixer based on the nonlinearity of a quasi-particle current in the SIS junction, a planar superconducting receiving antenna, and a cryogenic local oscillator, is described. Being dc-powered only by batteries, such a microcircuit operates as a submillimeter-wave superheterodyne receiver without any additional microwave equipment. Such receivers are very attractive for radioastronomical research, space communication systems, and monitoring of the environment from satellites, balloons, and special aircraft. A breadboard of a superconducting spectrometer with a phase-locked flux-flow oscillator (FFO) has been developed and tested. A frequency resolution better than 10 kHz was reached at a frequency of 365 GHz. We describe a balloon-borne 500-650 GHz integrated spectrometer for oblique atmospheric sounding, developed for the international Terahertz Limb Sounder (TELIS) project. The first flight is scheduled for 2005.     

Development of Josephson Traveling-Wave Parametric Amplifier Based on Aluminum SIS Junctions

Physics of the Solid State - Prototypes of the design of Josephson traveling-wave parametric amplifier based on aluminum superconductor–insulator–superconductor junctions in the form of...     

Zurek-Kibble mechanism for the spontaneous vortex formation in Nb-Al/Al(ox)/Nb Josephson tunnel junctions: new theory and experiment

New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched Nb-Al/Al(ox)/Nb annular Josephson tunnel junctions (JTJs) as a function of the quench time, tau(Q). The probability f(1) to trap a single defect during the normal-metal-superconductor phase transition clearly follows an allometric dependence on tau(Q) with a scaling exponent sigma = 0.5, as predicted from the Zurek-Kibble mechanism for realistic JTJs formed by strongly coupled superconductors. This definitive experiment replaces one reported by us earlier, in which an idealized model was used that predicted sigma = 0.25, commensurate with the then much poorer data. Our experiment remains the only condensed matter experiment to date to have measured a scaling exponent with any reliability.     

Electron and phonon effects in superconducting tunnel detectors of x-radiation

Nb/Al/AlO_x/Nb superconducting tunnel junctions were investigated in the role of x-ray detectors. Amplitude spectra of pulses arising upon irradiation of tunnel junctions of different sizes by ⁵⁵Mn x-radiation were recorded at a temperature T=1.4 K. We also analyzed the temporal shape of the pulses. We considered the influence of diffuse motion of nonequilibrium quasiparticles, the inverse tunneling effect, and exchange of 2Δ phonons between electrodes, on the characteristics of the tunnel detectors. It is shown that phonon processes can bring about changes in the amplitude, duration, and polarity of the signal. Fiz. Tverd. Tela (St. Petersburg) 41, 1168–1175 (July 1999)     

Heat release in the cryogenic system of a superconducting integrated detector and the influence of heat on its operation

Heat release in the cryogenic system of a subterahertz-range superconducting integrated detector at ≈4.2 K is studied, and the influence of the released heat on its main characteristics is estimated. The detector chip mounted on a silicon lens is connected to a bias board by aluminum wires 25 μm in diameter, which are fixed by ultrasonic bonding. They are necessary for setting a bias current through the working components of the detector and represent an integral part of the system. The contact resistance between the wires and contact pads of the microchip is measured. The contact resistance is found to considerably exceed the resistance of the aluminum wire and, hence, makes a major contribution to heat release in the system. A “multipoint contact with one wire” technique is suggested. Tests show its efficiency: the contact resistance decreases considerably compared with the standard approach.     

Josephson Tunnel Junctions with an Integral Superconductor–Insulator–Normal Metal Shunt

Physics of the Solid State - This study is devoted to the investigation of tunneling superconductor–insulator–superconductor (SIS) Josephson junctions with a new type of shunt based on...     

Developing topologies of thin-film SQUID sensors for measuring extremely subtle magnetic fields

A topology of thin-film SQUID sensors that are based on Nb/AlO_x/Nb tunnel junctions has been developed and optimized for nondestructive testing of materials and for other systems with a magnetic field sensitivity of <10 fT/Hz^1/2.