Nanomechanical Detection of Vortices in an Electron Fluid.

Electron vortices are an expected manifestation of viscosity, yet their detection remains challenging. We introduce a nanomechanical paradigm: a vortex in a suspended resonator generates a magnetic moment that, in an in-plane field, drives vibrations via magnetic torque. Using a comparative design with a reference device where vortices are suppressed, we provide unambiguous identification of the circulating flow. We detect ballistic and hydrodynamic vortices and trace their temperature crossover. Our work establishes nanomechanics as a direct force-sensing platform for electron hydrodynamics.