Cutting the pyrochlore – boundary conditions on quantum spin ice

Quantum spin ice is famous for its ability to host an emergent electromagnetic field, with gapless low-energy excitations that take the form of emergent photons. Starting from a microscopic description, and considering a set of different terminations of the pyrochlore lattice, we derive boundary conditions on the emergent electromagnetic fields. Some choices of termination naturally leave emergent charges on the boundary, whereas others do not – leading to boundary conditions akin to those at conducting and insulating interfaces in conventional electromagnetism. Furthermore, we account for couplings to the "real" electromagnetic fields, and make predictions for how external electromagnetic waves behave when encountering the emergent electromagnetic fields inside quantum spin ice.