Seeing the light: Observing photons in quantum spin ice

Spin ice, with its magnetic monopole excitations, is perhaps the best studied example of a classical spin liquid. Quantum mechanical tunnelling between the classical ground states of spin ice leads to an exciting new scenario- a quantum spin liquid ground state with emergent photon excitations [1, 2]. Here we explore how this ``artificial electromagnetism'' would manifest itself in neutron scattering experiments on putative ``quantum spin ice'' materials. Using lattice gauge theory we make explicit predictions for the ghostly, linearly dispersing magnetic excitations which are the ``photons'' of this emergent electromagnetism. We find that ``pinch points,'' which are the signal feature of a classical spin ice, fade away as the system approaches its zero-temperature ground state. The predictions of this field theory are shown to be in excellent quantitative agreement with quantum Monte Carlo simulations at zero temperature~[3].\\[4pt] [1] M. Hermele, M. P. A. Fisher and L. Balents, Phys. Rev. B. {\bf 69}, 064404 (2004).\\[0pt] [2] L. Savary and L. Balents, Phys. Rev. Lett. {\bf 108}, 037202 (2012).\\[0pt] [3] O. Benton, O. Sikora and N. Shannon, Phys. Rev. B. {\bf 86}, 075154, (2012).