Universal Spin Transport and Quantum Bounds for Unitary Fermions

Understand

We review recent advances in experimental and theoretical understanding of spin transport in strongly interacting Fermi gases.

• The central new phenomenon is the observation of a lower bound on the (bare) spin diffusivity in the strongly interacting regime.
• Transport bounds are of broad interest for the condensed matter community, with a conceptual similarity to observed bounds in shear viscosity and charge conductivity.
• We discuss the formalism of spin hydrodynamics, how dynamics are parameterized by transport coefficients, the effect of confinement, the role of scale invariance, the quasi-particle picture, and quantum critical transport.