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Sunday, November 14

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Friday, January 8

  1. 8:50 am

Wednesday, January 6

Wednesday, November 11

  1. msg papers written or published under the higehr Tc KITP program message posted papers written or published under the higehr Tc KITP program Dear participants of the Higher Tc KITP Program We are in the process of writing our report on t…
    papers written or published under the higehr Tc KITP program
    Dear participants of the Higher Tc KITP Program

    We are in the process of writing our report on the Higher Tc Superconductivity Program. we will be grateful if you would send us a list and/or pdf files of manuscripts that you wrote or published during your stay at KITP. Please send me your files (or emails) to my regular email: efradkin@illinois.edu

    Thank you

    Eduardo Fradkin
    6:31 pm

Tuesday, September 8

  1. page Social Activities edited On this page, please post any dinners, hikes, trips to wineries, surf lessons, or suggestions that …
    On this page, please post any dinners, hikes, trips to wineries, surf lessons, or suggestions that other people in the group might like to do.Instead of keeping track of and exchanging email messages, you can simply ask people to sign up here!
    Colleagues:
    This evening our weekly dinner will be at The Beach House around 6pm. The Beach House is located at Goleta Beach and is an easy walk from KITP. If you are going, please sign up below, so that we can get an accurate count.
    Thanks
    Name:
    Catherine Kallin
    H R Krishnamurthy
    Gertrud Zwicknagl + husband
    Ivar Martin
    Alex Gurevich

    (view changes)
    7:48 pm
  2. page Social Activities edited ... like to do. Instead do.Instead of keeping Colleagues: This evening our weekly dinner wi…
    ...
    like to do.
    Instead
    do.Instead of keeping
    Colleagues:
    This evening our weekly dinner will be at The Beach House around 6pm. The Beach House is located at Goleta Beach and is an easy walk from KITP. If you are going, please sign up below, so that we can get an accurate count.
    ...
    Ivar Martin
    Alex Gurevich
    Sasha Chernyshev + Lena + Vanya + Andrey
    (view changes)
    2:44 pm

Thursday, September 3

  1. page Program Questions and Comments edited ... 8.1 What is the evidence- theoretical or experimental – that spin liquid physics is actually b…
    ...
    8.1 What is the evidence- theoretical or experimental – that spin liquid physics is actually beneficial for superconductivity?
    Balents: I asked this question because the situation seems somewhat mixed. RVB theory remains a major candidate in the cuprates. At least at the level of variational wavefunctions for the superconducting state, it seems to be quite successful. It also historically gave a simple picture (within slave bosons, for instance) for the difference between the pairing and phase coherence scales, which is related to the pseudogap. However, the general idea of doping a spin liquid as a mechanism for superconductivity does not seem to be very robust experimentally, so far. In the cuprates, one has antiferromagnetism at low doping, and one can invoke magnetic fluctuations rather than spin liquid physics. In other materials, spin liquids have been hard to find, and when we do, they do not seem to be especially beneficial for superconductivity. An interesting experimental comparison can be made in the kappa-ET organics, where one can compare a spin liquid material and an antiferromagnetic one. The two materials differ very little structurally. On applying pressure, both become superconducting, but as Kanoda described in the conference, the superconductivity seems stronger in the antiferromagnetic one. The 3d hyperkagome material, Na4Ir3O8, which appears to be a spin liquid, has recently been hole doped by Takagi using Na deficiency, and does not become superconducting, at least above 0.5K or so.
    ...
    be hopeful!
    {full-CDMFT-phase-diagram.jpg} CDFMT Phase Diagram
    Tremblay: This phase diagram is for the zero-temperature half-filled square lattice t-t'-U Hubbard model. The region marked spin liquid within CDMFT just corresponds to a region where simple magnetic order is not found. The d-wave superconductivity is separated by a first order Mott transition from that "spin liquid" phase.
    This{phase_diagram.jpg} BEDT Lattice
    This
    is analogous
    ...
    (BEDT lattice). Alth {phase_diagram.jpg} BEDT LatticeoughAlthough it does
    ...
    on that plot ,plot, the strongest
    8.2 If exotic physics is behind higher Tc superconductivity, can it give some guidance for the search for new materials? Is two-dimensionality important? Low spin?
    8.3 Many exotic states seem almost to be defined by their featureless appearance when viewed with standard experimental techniques. Can you suggest what kind of experiment might provide a clear smoking gun signature? Can the problem benefit from improvements in spectroscopic or local probes?
    (view changes)
    10:14 pm
  2. page Program Questions and Comments edited ... Balents: I asked this question because the situation seems somewhat mixed. RVB theory remains …
    ...
    Balents: I asked this question because the situation seems somewhat mixed. RVB theory remains a major candidate in the cuprates. At least at the level of variational wavefunctions for the superconducting state, it seems to be quite successful. It also historically gave a simple picture (within slave bosons, for instance) for the difference between the pairing and phase coherence scales, which is related to the pseudogap. However, the general idea of doping a spin liquid as a mechanism for superconductivity does not seem to be very robust experimentally, so far. In the cuprates, one has antiferromagnetism at low doping, and one can invoke magnetic fluctuations rather than spin liquid physics. In other materials, spin liquids have been hard to find, and when we do, they do not seem to be especially beneficial for superconductivity. An interesting experimental comparison can be made in the kappa-ET organics, where one can compare a spin liquid material and an antiferromagnetic one. The two materials differ very little structurally. On applying pressure, both become superconducting, but as Kanoda described in the conference, the superconductivity seems stronger in the antiferromagnetic one. The 3d hyperkagome material, Na4Ir3O8, which appears to be a spin liquid, has recently been hole doped by Takagi using Na deficiency, and does not become superconducting, at least above 0.5K or so.
    So does this mean RVB as a superconducting mechanism is wrong? I tend to think it is not so simple. One possibility is that RVB superconductivity requires the "right" kind of spin liquid. It is pretty clear that the spin liquid should have a preformed pair gap to get a superconductor on doping. Not all spin liquids have this. The organic material seems, at least above say 5K, to be described by the "spinon Fermi sea" type of spin liquid. In this state, the spinons are not paired, and there is no gap. So doping this thing doesn't naturally give a superconductor (it gives a metal, actually). In general, such a spinon Fermi sea state is most likely close to the Mott transition. So perhaps a speculation is that for RVB superconductivity requires a spin liquid not too close to the Mott transition. Maybe the kagome antiferromagnets that have studied recently are better candidates. They haven't been doped yet, but we can be hopeful!
    {full-CDMFT-phase-diagram.eps} Tremblay:{full-CDMFT-phase-diagram.jpg} CDFMT Phase Diagram
    Tremblay:
    This phase
    ...
    liquid" phase. This
    This
    is analogous
    ...
    (BEDT lattice). {phase_diagram.eps} AlthoughAlth {phase_diagram.jpg} BEDT Latticeough it does
    ...
    on that plot,plot , the strongest
    8.2 If exotic physics is behind higher Tc superconductivity, can it give some guidance for the search for new materials? Is two-dimensionality important? Low spin?
    8.3 Many exotic states seem almost to be defined by their featureless appearance when viewed with standard experimental techniques. Can you suggest what kind of experiment might provide a clear smoking gun signature? Can the problem benefit from improvements in spectroscopic or local probes?
    (view changes)
    10:04 pm

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