Some Aspects of Coulomb Spin Liquids

The competing interactions in highly frustrated magnets often lead to
very interesting emergent phases that are not possible in conventional
antiferromagnets. An example of such a phase is the classical "Coulomb
spin liquid" which for example, occurs in spin ice compounds that have
and continue to generate much interest in the magnetism community as
an experimental realization of emergent "magnetic monopoles".  A
crucial signature of the Coulomb phase is the unusual *pinch-point*
shape of the spin structure factor in momentum space which is
experimentally accessible through neutron scattering. I will discuss a
theory for the full spin structure factor across a range of settings
which establishes the fate of the pinch points at low and high
temperature, for Ising and Heisenberg spins, for short- and
long-ranged (dipolar) interactions, as well as in the presence of
disorder. One striking prediction of this theory is that the
pinch-point singularities are present even at finite temperature and
disorder and not smeared out for spin ice compounds. I will also
discuss how putting non-magnetic disorder in spin ice induces a very
interesting spin glass phase where the freezing and the topological
spin ice phase are inseparably entangled: spins missing due to the
dilution become effective degrees of freedom that undergo freezing at
low temperatures, with the fluctuating background spin liquid
contributing towards the interaction of the hole-spins.