Special QM Seminar Speaker Xue-Yang Song (Harvard), Thursday, November 19 at 4:00 pm

Host Ehud Altman
Time/Venue Thursday, November 19 at 4:00 pm Pacific Time via this Zoom link
Talk Title Dirac spin liquids on the square, kagome and triangular lattices: Unified theory for 2D quantum magnets and doped electronic phases
Abstract Quantum magnets provide the simplest example of strongly interacting quantum matter, yet they continue to resist a comprehensive understanding above one spatial dimension. We explore the Dirac spin liquid (DSL) on 2D lattices, a version of Quantum Electrodynamics (QED3) with four flavors of Dirac fermions coupled to photons. Importantly, its excitations include magnetic monopoles that drive confinement, and the symmetry actions on monopoles contain crucial information about the DSL states. The underlying band topology of spinon insulators, e.g., wannier insulator protected by rotation etc, determines the elusive Berry phase of monopoles.  The stability of the DSL is enhanced on triangular and kagome lattices compared to square(bipartite) lattices. We obtain the universal signatures of the DSL on triangular and kagome lattices, including those of monopole excitations, as a guide to numerics and experiments on existing materials. Even when unstable, the DSL helps unify and organize the plethora of competing orders in correlated two-dimensional materials.
Time permitting I will describe recent results on chiral spin liquid states on the triangular lattice and the superconducting/metallic phases that emerge on lightly doping them.

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