Chiral kinematic theory and converse vortical effects

Response theories in condensed matter typically describe the response of an electron fluid to external electromagnetic fields, while perturbations on neutral particles are often designed to mimic such fields. Here, we study the response of fermions to a space-time-dependent velocity field, thereby sidestepping the issue of a gauge charge. We first develop a semiclassical chiral kinematic theory that contains a subtle modification of the phase space measure due to the interplay between the Berry curvature and fluid rotation. The theory immediately predicts a converse vortical effect, defined as an orbital magnetization driven by linear velocity. It receives contributions from magnetic moments on the Fermi surface and Berry curvature of the occupied bands, with the latter stemming from the modified measure. Then, transcending semiclassics via a complementary Kubo formalism reveals that the uniform limit of a clean system receives only the Berry curvature contribution, thus asserting the importance of the modified measure, while other limits sense the Fermi surface magnetic moments too. We propose CoSi as a candidate material, and we suggest conducting magnetometry measurements on a sample under a thermal gradient to detect the effect. Overall, our study sheds light on the effects of a space-time-dependent velocity field on electron fluids and paves the way for exploring quantum materials using new probes and perturbations.