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  • The Electronic Aladdin Newsletter

    No.5 May 1996

    1)News from the HiTc Frontier

    Two recent publications in Science and Physical Review Letters demonstrate the latest progress in understanding high temperature superconductivity from high resolution photoemission experiments.

    Kelley and coworkers address the doping dependence of the superconducting gap. One of the fundamental issues in high temperature superconductors is the nature of this gap, which serves as the order parameter of the system. Conventional superconductors have an isotropic order parameter, i.e. the gap is independent of the direction that the electrons travel in the crystal (s-wave superconductivity). The HiTc materials, in contrast, seem to display d-wave superconductivity, where the gap goes from a maximum to zero every 45 degrees. The experiments by Kelley et. al. (Science 271, 1255, 1996) show that this angle-dependent gap variation also depends on the doping level. At optimum doping, the variation is 20:1, but at overdoped levels it is reduced to 2:1. Thus, it appears as if the order parameter changed from one symmetry to the other with doping.

    The other study looks at the energy band structure of HiTc superconductors and, in particular, at possible traces of magnetic interactions affecting the band structure. Many current theories of HiTc superconductivity are based on magnetic interactions giving rise to superconducting pairs of electrons in contrast to the lattice vibrations (or phonons) that give rise to superconducting pairs in conventional superconductors. The detailed band structure study of the 2-2-1-2 HiTc superconductor published by Ding et. al. (Phys. Rev. Lett. 76, 1533, 1996) found indeed that there are so called "shadow bands" which are derived from the normal bands by momentum transfer at a local antiferromagnetic order. This type of complete band structure study is essential for obtaining the maximum amount of experimental information in order to discriminate between a large number of different theories.

    2)Users' Meeting Date Up For Approval

    During the last few months, members of the Users Advisory Committee and SRC management have discussed different scenarios for a new format of the annual Users' Meeting. According to a recent poll, many SRC users did not attend the annual meeting in the past due to time constraints and limited travel budget. One possibility for a new setting of the Users' meeting, which minimizes travel cost and time, could be a get together on the Sunday before the APS March Meeting which is regularly attended by the majority of SRC's users. The next APS March meeting is scheduled to be held in Kansas City, Missouri on March 17-21, 1997. As a consequence of the date change, the Aladdin Lamp Award would also be awarded at a dinner session on March 16 and the application deadline would be set back to December 31, 1996. Before finalizing this move we would like to collect comments and suggestions. (send your input to Pam Layton, e-mail: playton@src.wisc.edu)

    3)"Town Meeting" Called

    On May 13 the magnetron tube in the microtron rf system failed. Since the spare tube was already at the factory awaiting repairs, SRC was left with the tube from the old Tantalus microtron, which is now installed at the Aladdin microtron. Stored beams in Aladdin have been reduced to 100 to 150 mA. The rebuilt tube should be delivered around the end of July.

    Various options to improve the lifetime of the smaller stored beams in Aladdin were discussed at a user's "town hall" meeting on Wednesday, May 29. Those in attendance agreed that SRC will continue to use the Tantalus tube, which is currently installed, until the failed tube can be rebuilt, or a spare tube of known quality can be obtained. An update will be given to the users at the next scheduling meeting on Monday, June 3, at noon in the conference room.

    SRC staff are also considering scheduling more 1 GeV beams to take advantage of the inherent longer lifetime.

    4)Internet Job Board For SR-Community

    Hartmut Hochst has created a pinboard on his website for open/wanted job positions in the SR-community. Postings from students who are looking for a position are also encouraged.

    5)Operations Summary for May 31 - June 30

    00:00-08:0008:00-12:0012:00-24:00
    May 311 GeV Beam Optional 800 MeV Beam
    June 011 GeV BeamNo BeamNo Beam
    June 02No BeamNo BeamNo beam
    June 03No BeamOptional800 MeV Beam
    June 041 GeV BeamOptional800 MeV Beam
    June 051 GeV BeamOptional800 MeV Beam
    June 061 GeV BeamOptional800 MeV Beam
    June 071 GeV BeamOptional800 MeV Beam
    June 081 GeV BeamNo BeamNo Beam
    June 09No BeamNo BeamNo Beam
    June 10No BeamOptional800 MeV Beam
    June 111 GeV BeamOptional800 MeV Beam
    June 121 GeV BeamOptional800 MeV Beam
    June 131 GeV BeamOptional800 MeV Beam
    June 141 GeV BeamOptional800 MeV Beam
    June 151 GeV BeamNo BeamNo Beam
    June 16Start of SRC WEEKVault Closed
    June 17Vault Closed
    June 18Vault Closed
    June 19Vault Closed
    June 20Vault Closed
    June 21Vault Closed
    June 22End of SRC WEEKVault Closed
    June 23Start of QuantumNo Beam
    June 24No BeamOptional800 MeV Beam
    June 251 GeV BeamOptional800 MeV Beam
    June 261 GeV BeamOptional800 MeV Beam
    June 271 GeV BeamOptional800 MeV Beam
    June 281 GeV BeamOptional800 Mev Beam
    June 291 GeV BeamNo BeamNo Beam
    June 30No beamNo BeamNo Beam