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We discuss results on the superconducting, electron-transport, and tunneling properties of Al doped with Mn in the range of 1000 to 3000 ppm. We demonstrate that the critical temperature of Al can be systematically reduced to below 50 mK. Films are prepared by sputter deposition, and show values of d(ln R)/d(ln T) of ∼500, indicating sharp superconducting transitions. Al-Mn/I/Al-Mn tunnel junctions show low sub-gap conductance and BCSlike characteristics. Our results in general suggest that the material is of interest for transition-edge sensors operating in the 100 mK regime and superconductor/insulator/superconductor (S/I/S) and normal/insulator/ superconductor (N/I/S) devices, in the latter case where heavily doped Al-Mn can replace the normal metal. [ABSTRACT FROM AUTHOR]

Multiplexed readout is a requirement for the successful deployment of large-scale cryogenic detector arrays in applications ranging from x-ray microanalysis to sub-millimeter astronomy. We report on the development of a time-division SQUID multiplexer (SQUID MUX) to read out one column of a 32 × 32 transition-edge sensor (TES) array. The new SQUID MUX has three stages. Individual TES pixels inductively couple to first-stage SQUID's, which are summed and coupled to a second-stage SQUID via a superconducting transformer. The first- and second-stage SQUID's are integrated on the same chip and are operated at the working temperature of the detectors of about 100 mK. The second stage SQUID is read out by a SQUID series array at 4K. Compared to former designs, the new SQUID MUX features a balanced input configuration to reduce crosstalk between read-out channels. In this paper we discuss the SQUID MUX design and analyze the noise and bandwidth performance of the SQUID multiplexer. Multiplexing of test input signals utilizing digital feedback electronics is demonstrated. [ABSTRACT FROM AUTHOR]

Bicrystal grain-boundary junctions (bi-GBJs) have been reproducibly fabricated on SrTiO/sub 3/ (STO) and r-plane Al/sub 2/O/sub 3/ (sapphire) bicrystal substrates. Sapphire bicrystals are candidates for high-frequency applications due to their low dielectric constant and loss tangent. The sapphire bi-GBJs demonstrated resistively shunted junction (RSJ)-like current voltage characteristics, with junction parameters comparable to the STO bi-GBJs and critical current densities Jc/spl sim/10/sup 5/ A/cm/sup 2/. Independent control of junction resistance (R/sub N/) was demonstrated with the use of Au shunt layers. In addition, overlayers such as Au or STO may act to passivate the GBJs and improve long term stability. [ABSTRACT FROM PUBLISHER]

Improved via connections in structures of YBa/sub 2/Cu/sub 3/O/sub 7-x//SrTiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO/STO/YBCO) multilayers have been made using a combined HF wet-etching and ion-milling process. The critical current density J/sub c/ of the via is as high as 2/spl times/10/sup 6/ A/cm/sup 2/ at 76 K, and is dominated by edge contacts in the ab-plane, YBCO and Sr/sub 2/AlNbO/sub 6/ (SAN) multilayer test circuits were also made with this process. The 4/spl deg/ crossovers in a SAN test chip had a critical temperature T/sub c/ of 88 K and J/sub c/ of 1.5/spl times/10/sup 6/ A/cm/sup 2/ at 81 K, very close to those of the planar film, showing no evidence of weak links in the YBCO crossing low angle SAN steps. [ABSTRACT FROM PUBLISHER]

Electrical noise measurements at 10 Hz are reported for YBCO films at the resistive edge. Results are given for films with widths of 0.1, 1, and 5 mm that were deposited simultaneously on the same substrate, for three different substrate materials. The NET improves by approximately a factor of 10 as the thermometer area is increased by a factor of 2500, with fixed bias current, At temperatures giving maximum dR/dT and with nominally 19 mA bias currents, the 5 mm samples have very low noise equivalent temperatures of 3.1, 3.5, and 4.4 nK//spl radic/Hz for LaAlO/sub 3/, Al/sub 2/O/sub 3/, and Si substrates, respectively. These are the lowest values reported up to the present time. Surprisingly, noise from the sample on Si is consistent with pure Johnson noise even with bias Current as large as 5 mA (0.28/spl times/10/sup 4/ A/cm/sup 2/). For YBCO thicknesses no greater than 50 nm excellent thermometers can be made on any of these substrates in spite of the mechanical strains produced in the films by the substrate. [ABSTRACT FROM PUBLISHER]

We present results on the responsivity of YBCO thin-film devices to mid-infrared (25 /spl mu/m) radiation. Light is generated by pulsed diode-laser sources monitored by a calibrated HgCdTe detector. For the sample geometry studied here, we estimate an upper limit to the low-frequency responsivity, R of /spl sim/1000 V/W. [ABSTRACT FROM PUBLISHER]

Examines high temperature superconducting Josephson junctions in a stacked bicrystal geometry. Observations of weak link behavior in the bridges formed; Measurement of characteristic voltages; Display of resonant structure in the current-voltage characteristics of the upper-layer junctions.

Investigates mutual phase locking in two-junction systems of high temperature superconductor-normal metal-superconductor junctions. Use of the two-junction circuit with a nonsuperconducting feedback path; Characterization of the strength of the phase-locked state; Relation between locking strength and temperature.