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  1. M

    Spin liquid states and conductors

    Hi, All articles on spin liquids I've seen treat them as insulators. This is understandable in the context in which they were first introduced i.e. the resonating valence bond state in which every electron is singlet-ed with every other, and thus essentially blocking conduction. Given...
  2. M

    U(1) symmetry breaking within the superluid phase

    Hi With the Bose-Hubbard Hamiltonian (BHH) being invariant under a U(1)\equivO(2) symmetry transformation, it is said that the hopping-term in the BHH tends to break the U(1) symmetry as the system leaves the insulating phase. This is not clear to me. However within the mean-field...
  3. M

    Singlet sharing

    Hello I have come across this inexplicable fact mentioned in somewhere that for a chain of S = 1 spins, the adjacent bonds can all be in a singlet state i.e. singlets can be shared in this case (forming valence bond solids) but not, for example, for |S| = 1/2, the latter point being clear. I...
  4. M

    Question on universailty classes

    Hi When a particular model (say Ising) is solved on a particular lattice (say 2D triangular), do the critical exponents of the same model fall within the same universality class (have same critical exponents) as when solved on a different lattice (say 3D cubic)? Thanks, Mavi
  5. M

    Opening up of spin gap

    Hi Can somebody explain what is a "gapless excitation"? If it is an excitation, why does it require no energy (gapless) to excite the system? Thanks, Mavi
  6. M

    Instability of Fermi surface

    Hi Can somebody explain the meaning of the following sentence which is from Wikipedia: "Solids with a large density of states at the Fermi level become unstable at low temperatures and tend to form ground states where the condensation energy comes from opening a gap at the Fermi surface e.g...