Multipolar orders in quantum magnets

Traditionally, magnetism in solids deals with ordering patterns of the electron magnetic dipole moment, as probed, for instance, via neutron diffraction. However, materials such as f-electron heavy fermion systems are well-known candidates for more complex forms of symmetry breaking, involving higher-order magnetic or electric multipoles, often termed as "hidden orders". In this talk, I will discuss our recent theoretical proposal for Ising octupolar order in d-orbital systems, which appears to explain a wide range of experiments in certain 5d transition metal oxides with spin-orbit coupling. The proposed Ising ferro-octupolar order is shown to be linked to a type of orbital loop-current order. We propose NMR experiments under strain as a further test of our proposal. This appears to be the first candidate for d-orbital octupolar order.