Frustration

=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