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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. Spin ice ground states are highly degenerate yet locally constrained and in the absence of monopole excitations, effectively no dynamics is possible. At low temperatures, the monopoles are sparse and dynamics becomes very slow. These systems are therefore prone to falling out of equilibrium at low temperatures, for instance following comparatively rapid changes in temperature or applied magnetic field. In this regime, a wealth of dynamical phenomena occur, including reaction diffusion behaviour, slow dynamics due to kinematic constraints, as well as behaviour that mimic the deposition of interacting dimers on a lattice. The situation is further complicated by the presence of disorder that, even at small densities, appears to have a sizeable effect on the low-temperature dynamics of these systems. Here we investigate some of these phenomena and we propose how to effectively extend existing theories to describe spin ice out of equilibrium. Nonequilibrium physics in spin ice is a novel setting which combines kinematic constraints, emergent topological defects, and magnetic long range Coulomb interactions.

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Claudio Castelnovo, University of Cambridge
Seminar Room of the Institute of Physics II (R201)
Contact: Simon Trebst