Spin motive force by the momentum-space Berry phase in magnetic Weyl semimetals

Electrons with topologically non-trivial band structures show unique phenomena reflecting their topological nature. For instance, in recent years, studies on the transport and optical properties of Weyl semimetal discovered the photovoltaic effect reflecting the Berry phase and magnetoresistance related to chiral anomaly. In addition, the experimental discovery of magnetic Weyl semimetals opened a route to study novel phenomena arising from the interplay of Weyl electrons and magnetism. Drawing inspiration from the adiabatic charge pump, we explore how the dynamics of the magnetic moment and the Berry phase arising from the dynamics affect the material properties. We show that the precession of ferromagnetic moment in a Weyl semimetal induces a Berry curvature with the time derivative, similar to the adiabatic pump. This phenomenon resembles Faraday's law of electromagnetism, in which the circular electric current induces a magnetic field; the circular motion of the Weyl node, a magnetic charge in the momentum space, induces a momentum-space electric field that appears in the adiabatic pump. The Berry phase effect results in a macroscopic current in a setup similar to the ferromagnetic resonance, in which the current appears as a spin motive force. Unlike the conventional spin motive force, this phenomenon produces a finite current without a magnetic gradient. The result shed light on a novel material property arising from the Berry phase effect and its potential for spintronics application.