Physics (Internal)

Seeing beyond the light: Vison and photon electrodynamics in quantum spin ice

This event is part of the Condensed Matter Theory Seminar Series.

Understanding the nature and behaviour of excitations in quantum spin liquids, and in topological phases of matter in general, is of fundamental importance and has proved crucial for experimental detection and characterisation of candidate materials. Current theoretical and numerical techniques, however, have limited capabilities, especially when it comes to studying gapped excitations. In this talk, I will discuss a semiclassical numerical method, based on large-$S$ path integral approach, to study a wide class of systems whose spin liquid behaviour is underpinned by perturbative ring-exchange Hamiltonians. Our method can readily access both thermodynamic and spectral properties.

I will focus in particular on quantum spin ice and its photon and vison excitations. After benchmarking the method against existing results on photons, we used it to characterise visons and their thermodynamic behaviour. We find that visons form a weak electrolyte -- in contrast to spinons in classical spin ice --, that is, vison pairs are the dominant population at low temperatures. This is reflected in the behaviour of thermodynamic quantities, such as pinch point motifs in the relevant correlators. Moreover, visons appear to strongly hybridise with the photon background, a phenomenon that gravely affects the way these quasiparticles may show up in inelastic response measurements.

We believe that generalisations of our method can substantially extend our understanding of quasiparticles and their interplay in quantum spin ice and other quantum spin liquids, quantum dimer models, and lattice gauge theories in general.