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Three-Terminal Tunnel-Junction Device Employing Energy-Gap Control in Superconducting Electrodes

IP.com Disclosure Number: IPCOM000059960D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Epperlein, PW: AUTHOR

Abstract

Magnetically controlling the energy gap of a two-film, single-junction device permits the simple device to act as a three-terminal "superconducting transistor." The basic configuration is the known tunnel junction formed in the overlap region of two, crossed, superconducting striplines (Fig. 1). The configuration should be placed over a superconducting ground plane in the usual way as in the Josephson technology. The magnetic field Hcont will be produced by a current Icont flowing through one of the device's electrodes (width w), preferentially the base electrode. The maximum magnetic field will be given by Hcont = Icont/w.

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Three-Terminal Tunnel-Junction Device Employing Energy-Gap Control in Superconducting Electrodes

Magnetically controlling the energy gap of a two-film, single-junction device permits the simple device to act as a three-terminal "superconducting transistor." The basic configuration is the known tunnel junction formed in the overlap region of two, crossed, superconducting striplines (Fig. 1). The configuration should be placed over a superconducting ground plane in the usual way as in the Josephson technology. The magnetic field Hcont will be produced by a current Icont flowing through one of the device's electrodes (width w), preferentially the base electrode. The maximum magnetic field will be given by Hcont = Icont/w. (1) According to the Ginzburg-Landau theory, the gap W goes continually to zero with increasing parallel magnetic field, when the film thick ness t gL, the London penetration depth, giving a second-order phase transition at the critical field Hc . The initial slope in this dependence is highest for t/gL . 0, and decreases with t/gL > 0. In thin, perturbed films, gL has to be replaced by geff, which is enhanced due to a reduced electron mean free path >local (London) theory). In the limit t < g, the gap varies at a temperature T < Tc with the field as

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for type-I superconductors, Tc . superconductor transition temperature (Fig. 2). It is proposed to use materials with low Hc(T) values, in order to achieve the biggest W-reduction for a certain applied Hcont, i.e., low Icont in the mA-range. Certainly, there are materials like Al or Sn with Hc(0) values in the order of 200 Oe, but these materials have Tc values below the liquid He temperature of 4.2 K, which for practical reasons should be the operating temperature of superconducting devices. To find low Hc(0) materials with Tc > 4.2 K, only the Hc(0) values of various materials were compared, but still it was kept in mind that the critical field of a thin film is bigger than the thermodynamic field Hc(0) if t <<
g. Appropriate superconducti...