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5 Jan 1998

Volume 72, Issue 1, pp. 1-133

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Reduction of flux creep by heat pulses

G. A. Levin, C. C. Almasan, D. A. Gajewski, and M. B. Maple

Appl. Phys. Lett. 72, 112 (1998); http://dx.doi.org/10.1063/1.120661 (3 pages) | Cited 3 times

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We investigated the possibility of reducing the giant flux creep in high-temperature superconductors by temporarily increasing the temperature T above the operating temperature T0, after the critical state is created at T0. This T increase leads to a supercritical state which decays rapidly so that, when T is decreased back to T0, the superconductor is in the subcritical state. We have found that both the maximum persistent current and the relaxation rate are hysteretic and differ substantially from the corresponding quantities measured after flux annealing. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
61.72.Cc Kinetics of defect formation and annealing

Low noise multiwasher superconducting interferometer

P. Carelli, M. G. Castellano, G. Torrioli, and R. Leoni

Appl. Phys. Lett. 72, 115 (1998); http://dx.doi.org/10.1063/1.121444 (3 pages) | Cited 25 times

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The dc-superconducting quantum interference device (SQUID) is a low-noise converter from magnetic flux to voltage which can have, in principle, an energy sensitivity near the quantum limit of ℏ/2. A critical parameter for the ideal performance is the device inductance, which must be kept as small as possible. Minimizing the SQUID inductance, however, is a major concern for a practical device; this requirement implies a small SQUID ring and hence magnetic coupling with an external signal is more difficult to achieve. Here we present an original scheme (called multiwasher) to circumvent this problem, and its implementation in an all-refractory thin-film device. Our scheme not only provides good magnetic coupling with a large input coil (0.5 μH) and very low SQUID inductance, but also shielding from outside uniform fields, such as those generated by ambient disturbances. The measured coupled spectral energy sensitivity in the white region at about 1 kHz is 28ℏ at 4.2 K and 5.5ℏ in a pumped helium bath at 0.9 K. The flux noise spectral density at 0.1 Hz and 0.9 K is Φn = 1×10−6 Φ0/math. © 1998 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
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