Condensed Matter/Materials & Biological Physics Seminar with Arun Paramekanti on Multipolar symmetry breaking: Orbital and spin altermagnets

In contrast to dipole orders, multipole orders involve symmetry breaking patterns of higher multipoles involving spin and orbital moments. In this talk, I will discuss how a class of multipolar orders are closely connected to the recently proposed concept of altermagnets, and to earlier ideas of `nematic-spin-nematic' order by Kivelson, Fradkin, and co-workers, and certain types of loop current orders. I will highlight our theoretical proposal of octupolar order in a class of "5d"-Mott insulators with strong spin-orbit coupling which host non-Kramers doublets, and discuss the coupling of strain, impurities, and phonons to such multipolar orders. Our theory explains recent NMR and muSR experiments in these osmate double perovskites. Time permitting, I will discuss our work on multiorbital  tJ models which exhibit a rich phase diagram with weak/strong altermagnet orders and unconventional superconductivity.