Questions/topics for the Frustration Discussion

General Issues:

  • What is frustration good for?
    • Sensitivity to weak perturbations: maybe can control magnetism (and other orders) by engineering these?
    • Obtain coexisting or complex orders that do not otherwise exist?
    • Can we make any specific suggestions? e.g. multiferroics?
  • Cooperative paramagnets = spin liquids
    • General question: what is the description of systems which are disordered but strongly correlated well below their characteristic coupling scale, e.g. for magnets the Curie-Weiss temperature?
    • U(1) "Coulomb" states with dipolar correlations, such as pyrochlore antiferromagnet, spin ice
      • Is there interesting physics in ordering?
      • Defects, spin glass behavior - is it different from unfrustrated systems?
    • Are there other types of classical spin liquids?
    • Quantum spin liquids
      • In general (spin-)gapless quantum spin liquids are poorly understood. This is a pity since the most promising candidate materials must be gapless if they are indeed QSLs.
      • Gapped RVB states - any candidates? Where to look? Magnetization plateaus?
      • Numerical methods - do we need new ones?
      • Gauge mean field/variational methods - are they reliable, and how can one gain confidence?
      • Claim (Nagaosa during conference) that quanutm fluctuations can be large even for s=5/2 in non-collinear magnets.
  • Criticality
    • Various proposal for "exotic" quantum criticality - are they correct?
    • How about unusual criticality in the classical regime?
  • Frustration of other degrees of freedom
    • Orbital frustration -
      • Are there spin-orbital liquids?
      • Does Jahn-Teller always spoil frustration?
    • Charge frustration
      • Can be realized in simple models of lattice bosons (cold atoms)
      • Is this operative near the metal-insulator transition? In general, is a frustrated metal a good concept?

Materials specific issues

  • Quantum spin liquid candidates
    • Organics: kappa-BEDT (+ others?)
      • issue: what is the relationship between the spin liquid state and superconductivity?
    • Herbertsmithite
    • volborthite
    • SCGO
    • Na3Ir4O7
    • NiGa2S4
    • He3 on graphite
  • Complications with the above
    • Can spin-orbit be neglected? If not, how much is left of the spin liquid physics?
    • Dilution/disorder may not be so small.
  • Metallic spin liquids (not so clear what this means)
    • Short-range helimagnetism: MnSi - T^(3/2) behavior of resistivity
    • Pr2Ir2O7
    • NiS2 - T^(3/2) behavior seen here too.
  • Spin glass physics?
    • Ramirez at conference:
      • ubiquitous c ~ T^2 behavior (usual SG c ~ T)
      • strangely robust to high impurity concentrations x
      • Spin glass critical temperate independent of x?
    • Is there intrinsic SG behavior (disorder-free spin glasses)? or another scenario?
  • Magnetically-driven ferroelectricity
    • Spiral states very common in frustrated magnets