日時：2015年1月22日(木) 10:30 – 11:30
講師：Dr. Arnab Sen (Department of Theoretical Physics Indian Association for the Cultivation of Science)
題目：Correlations and glassiness in Coulomb Spin Liquids
要旨：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. 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.