Abstract

Spin ice materials such as Dy2Ti2O7 and Ho2Ti2O7 provide a rare instance of emergent gauge symmetry and fractionalisation in three dimensions. Their elementary excitations carry a fraction of the magnetic moment of the microscopic spin degrees of freedom, and they can be thought of as magnetic monopoles. This talk aims at introducing spin ice models and materials and reviewing their unusual properties. In particular, the peculiar nature of the excitations is discussed, together with (some of the) signatures that have been so far identified in the equilibrium and response properties of spin ice materials. These include unusual neutron scattering structure factors, dynamical arrest and long lived non-equilibrium metastable states, as well as a response to external magnetic fields that promotes spin ice as a magnetic analogue of an electrolyte. The formulation of the low-temperature phase in terms of an emergent gauge field permits an unusual degree of analytical progress in the modelling of these materials.