Experimental Insights into Quantum Spin Ice Physics in Dipole–Octupole Pyrochlore Magnets

We review a key subset of the experimental studies that have recently focused on cubic pyrochlore magnets whose pseudospin-1/2 degrees of freedom have mixed dipolar and octupolar character. We discuss how this comes about and how the character of the pseudospin-1/2 can be experimentally determined. The minimal spin Hamiltonian for such magnetic insulators is known to give rise to a rich phase diagram with both disordered U(1) quantum spin ice (QSI) states and all-in–all-out (AIAO) noncollinear ordered states, each with dipolar and octupolar character. We focus primarily on experimental studies on two such single crystal systems, the = 5/2 Ce 2 Zr 2 O 7 and the = 9/2 Nd 2 Zr 2 O 7 . We make the case that Ce 2 Zr 2 O 7 is an excellent QSI ground-state candidate material, close to the border between QSIs with dipolar and octupolar symmetry. Nd 2 Zr 2 O 7 exhibits an AIAO ordered phase, featuring an order parameter consisting of dipolar and octupolar magnetic moments. It is found to reside close to a QSI phase boundary and features dynamic fragmentation in its excitation spectrum.