Spectrum of itinerant fractional excitations in quantum spin ice

Understand

We study the quantum dynamics of fractional excitations in quantum spin ice.

• We focus on the density of states in the two-monopole sector, $\rho(\omega)$, as this can be connected to the wavevector-integrated dynamical structure factor accessible in neutron scattering experiments.
• We find that $\rho(\omega)$ exhibits a strikingly characteristic singular and asymmetric structure which provides a useful fingerprint for comparison to experiment.
• $\rho(\omega)$ obtained from exact diagonalisation of a finite cluster agrees well with that from the analytical solution of a hopping problem on a Husimi cactus representing configuration space, but not with the corresponding result on a face-centred cubic lattice, on which the monopoles move in real space.