Title: Superfluidity of Total Angular Momentum

Abstract: Spontaneous symmetry breaking of a U(1) symmetry leads to superfluidity of a corresponding conserved charge. We generalize the superfluidity to systems with U(1) symmetries acting on both matter fields and two-dimensional spatial coordinates. Such systems can be effectively realized in easy-plane ferromagnetic systems with spin-orbit coupling where the conserved charge is a total angular momentum. We clarify that under a steady injection of spin angular momentum, the superfluid of the total angular momentum shows spacetime oscillations of the spin density and geometry-dependent spin hydrodynamics. We also demonstrate that the steady spin injection destabilizes the superfluid of total angular momentum, causing a dissipation effect in its spin hydrodynamic properties. Our study broadens the comprehension of superfluidity and sheds new light on the interplay between symmetries and phases of matter.