Controlling resonant spin photocurrent using magnetic field; application to a magnetoelectric oxide Cr2O3

We study the magnon spin photocurrent in effective spin models for Cr2O3, a material known for its magnetoelectric effect. Using nonlinear response theory, we show that magnon spin current can be generated by both linearly and circularly polarized electromagnetic waves via one-magnon processes. While linearly polarized waves induce a spin current even in the absence of a static magnetic field, circularly polarized waves lead to a spin current only when a static field is present, and the current reverses its direction upon field inversion. The distinct dependence on the external magnetic field and the contrasting responses to different polarizations allow the spin photocurrent to be differentiated from competing effects such as spin pumping or inhomogeneous heating, facilitating experimental verification. These results suggest that Cr2O3 is a promising candidate for experimental studies of magnon photocurrent.