Light-induced thermal spin current

Thermal generation of magnonic spin current by the spin Seebeck effect (SSE) and spin-polarized current by the anomalous Nernst effect (ANE) are fascinating phenomena in the field of spin caloritronics. In this paper, we investigate the thermal spin current driven by light in the framework of the SSE and the ANE. Unlike heating by electrical means, the spin current can be enhanced or reduced, and its sign can even be reversed, thanks to the intrinsic characteristic of the penetrating light. Most importantly, by reversing the direction of the incident light, we are able to separate the contributions from the interfacial and bulk temperature gradients to the transverse spin accumulation. Notably, although the overall spin signals are strongly influenced by the frequency of light, the interfacial and bulk spin Seebeck coefficients are intrinsic and frequency independent. Furthermore, with light excitation, we observe a nearly instantaneous steplike response for both the SSE and the ANE, highlighting the importance of spin-charge conversion by spin-orbit coupling for ultrafast spin caloritronics.