[Seminar] "Experimental signatures of quantumness in rare-earth pyrochlores" by Dr. Romain Sibille

[Speaker]

Dr. Romain Sibille from Paul Scherrer Institute

[Abstract]

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 geometrical 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. 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. Remarkably, the low-energy physics of this quantum spin ice state is predicted to be a lattice analogue of quantum electrodynamics. I present recent experimental results showing signatures of quantum spin liquid states in different rare-earth pyrochlore oxides.