Abstract: 

Spin liquids, despite their apparently featureless ground states, are exotic magnetic states which host fractionalised excitations and emergent gauge fields. Interestingly, quenched disorder can nucleate defects with unusual properties and thus reveal the hidden collective excitations of such states. In this talk, I will explain how disorder affects the physics of a prototypical frustrated magnet, dipolar spin ice, both at high and low temperatures and in fact leads to a new phase at low temperature. This "topological spin glass” phase shows signatures of both spin liquidity and glassiness. I will also describe a new cluster algorithm that allows us to study the continuous phase transition to the topological spin glass and reliably extract the critical temperature and exponents.