Magnetic systems with competing interactions often adopt exotic ground states, which can be relevant to study new physics in quantum matter . A recurrent ingredient to stabilize such phases is frustration, such as in pyrochlore oxides where rare-earth magnetic moments decorate a lattice of corner-sharing tetrahedra. An unusual spin liquid appears for example in the pyrochlore Ho2Ti2O7, which features a classical ‘spin ice’ short-range correlated state [2,3]. A local constraint – the 2-in-2-out ‘ice rule’ acting on each tetrahedron – leads to a manifold of degenerate ground states in which the spin correlations give rise to emergent magnetostatics . Spin flips violating the ice rule generate magnetic monopole excitations , a mobile magnetic charge regarded as a quasiparticle carrying half of the dipole moment. A quantum analogue of the spin ice state is predicted to be a special type of quantum spin liquid formed through the coherent superposition of spin ice configurations [6,7]. Remarkably, the low-energy physics of this quantum spin ice state is predicted to be a lattice analogue of quantum electrodynamics. I review recent results on tracking the experimental signatures of quantum mechanical ground states in the pyrochlores Pr2Hf2O7 [8-9] and Ce2Sn2O7 [10-11].
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Dr. Jitae Park
Dr. Dominic Hayward