"Hidden Orders" in quantum materials

In contrast to dipolar order, multipolar orders involve symmetry breaking patterns of higher multipoles involving spin and orbital moments and have been extensively explored in heavy fermion materials. In this talk, I will discuss how a class of multipolar orders are closely connected to the idea of altermagnets or `nematic-spin-nematic' order. I will highlight our theoretical proposal of octupolar order in a class of 5d oxide and halide double perovskites with strong spin-orbit coupling which host non-Kramers doublets, and the coupling of strain, impurities, and phonons to such multipolar orders. Our theory explains recent susceptibility, NMR, and muSR experiments and I will briefly discuss future directions including Raman scattering, surface magnetism, dynamics, and control. Time permitting, I will also discuss a class of multiorbital  tJ models which exhibit a rich phase diagram with weak/strong altermagnet order and unconventional superconductivity.

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