Research: Spectrum of itinerant fractional excitations in quantum spin ice

Quantum spin ice refers to a class of highly frustrated magnets on the pyrochlore lattice. In spin ice, the combination of lattice structure and spin-orbit coupling produces a highly degenerate classical ground state whose fractional excitations can be characterized as magnetic monopoles. Upon including quantum effects, the ground state becomes a U(1) quantum spin liquid, and the monopole excitations acquire mobility.

Here we study the quantum dynamics of fractional excitations in quantum spin ice. We focus on the density of states in the two-monopole sector, as this can be connected to the wavevector-integrated dynamical structure factor accessible in neutron scattering experiments, and compute it both numerically and by  analytically solving a hopping problem on a Husimi cactus representing configuration space. Our results underline the importance of treating both monopole and gauge degrees of freedom on equal footing and present a novel instance of dimensional transmutation.

M. Udagawa and R. Moessner,
Spectrum of itinerant fractional excitations in quantum spin ice,
Phys. Rev. Lett. 122, 117201 (2019) (arXiv)