Physics Colloquium: Douglas Natelson, Rice University

Angular momentum transport in magnetic insulators - a probe of quantum magnetism Magnetic interactions allow emergent collective excitations like magnons (quantized spin waves) to transport electronic angular momentum even in insulators, when charge degrees of freedom are localized. In recent years, electrical techniques based on the spin Hall effect and its inverse have made it possible to examine the excitation and propagation of spin angular momentum in magnetic insulators. This opens up new avenues for studying insulating quantum magnets, systems in which strong magnetic interactions and geometric frustration lead to competing ordered states and quantum fluctuations. Of particular interest are candidate quantum spin liquids, in which quantum fluctuations are theorized to prevent long-range order and lead to exotic fractionalized spin -carrying excitations. I will introduce the ideas and techniques, and I will show recent experimental results on thermally driven spin transport in two transition metal oxides and a Kitaev-like quantum magnet, finishing with an outlook at future opportunities.