Browse Prior Art Database

Magneto Optic Sensor for Vortices in a Superconductor

IP.com Disclosure Number: IPCOM000109059D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 3 page(s) / 123K

Publishing Venue

IBM

Related People

Gambino, RJ: AUTHOR [+3]

Abstract

Disclosed is a device for detecting a vortex or a bundle of vortices used as a storage bit in a superconducting vortex memory. A vortex storage system in which mobile vortices, the information bits, are moved in a shift register by currents and are read out by passing them under a Josephson junction which serves as a detector is proposed in (*). In this system, the presence or absence of a vortex or a vortex bundle represents binary "1" and "0." With the advent of the high Tc superconductors, the vortex storage system has become more practical both because it can be operated at liquid nitrogen temperature and because some of these compounds have very mobile vortices. This is evidenced by the observation that some high quality films and single crystals have low critical currents at 77~K.

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Magneto Optic Sensor for Vortices in a Superconductor

       Disclosed is a device for detecting a vortex or a bundle
of vortices used as a storage bit in a superconducting vortex memory.
A vortex storage system in which mobile vortices, the information
bits, are moved in a shift register by currents and are read out by
passing them under a Josephson junction which serves as a detector is
proposed in (*).  In this system, the presence or absence of a vortex
or a vortex bundle represents binary "1" and "0."  With the advent of
the high Tc superconductors, the vortex storage system has become
more practical both because it can be operated at liquid nitrogen
temperature and because some of these compounds have very mobile
vortices.  This is evidenced by the observation that some high
quality films and single crystals have low critical currents at 77~K.
This is particularly true of some of the Bi and Tl copper oxide
superconductor compositions in thin-film form.  Also, because the
vortex mobility (1/viscosity) increases as the normal state
resistivity decreases, the oxide superconductors are particularity
well suited since they tend to have few carriers and, therefore, a
high resistivity in the normal state.  The mobility is inversely
proportional to the upper critical field which means that these
devices will work best close to Tc where the critical field is low.

      One of the difficulties of using these superconductors is that
reliable Josephson detectors have not been successfully fabricated.
Disclosed is a device for the magneto-optic detection of a vortex
bundle eliminating the need for a Josephson junction detector.  The
detector, shown in Fig. 1, consists of a thin film of a magneto-optic
transducer 1 deposited on a reflector layer 2 which is, in turn,
deposited on the superconductor 3.  A suitable magneto-optic
transducer is a 2500 A thick film of EuS deposited by electron beam
evaporation from an EuS source.  A film of this thickness has a
Faraday rotation of 20 degrees at a wavelength of 6328 A in an
applied field of 31 kF at a temperature of 20~K.  The reflector is a
thin layer of silver deposited on a film of YBa2Cu3O7 which has been
prepared by laser ablation in a separate evaporator.  Other parts of
the detector consist of a coil 4 for applying a magnetic field
locally to the detector, a source of polarized light 5, a means 6 of
detecting the polarization state of the light reflected from the
surface and a magnetic field source (not shown) to apply a bias field
near the lower critical field Hcl.  The optical system used in a
magneto-optical recording head is suitable for this detector.  In
operation, the shift register is stepped by...