Oral: Spin Seebeck Effect in Graphene

The Spin Seebeck Effect (SSE) converts thermal energy into spin currents in ferromagnetic materials, establishing spin caloritronics, a field that studies thermoelectric phenomena mediated by spins. In metal/magnet bilayers, a thermal gradient excites magnetic dynamics, transferring angular momentum to conduction electrons and generating spin currents. Spin pumping (SP), driven by microwave irradiation, also generates spin currents by exciting magnetic dynamics via ferromagnetic resonance. SSE is thermally driven, while SP is coherently excited, and both share similar mechanisms.

This study develops a microscopic theory for SSE at the interface of a ferromagnetic insulator and graphene, using the Schwinger-Keldysh formalism. The large Landau-level separations of graphene enable the observation of Landau quantization at higher temperatures and lower magnetic fields. We examine SSE in graphene for quantum Hall and plane wave states, comparing spin currents generated by SSE and SP. The results show that SSE exhibits quantum oscillations similar to SP, with peak shifts due to higher-frequency thermally excited magnons.

This framework offers insights into spin-thermal interconversion in atomic-layer materials, supporting the development of spin caloritronic devices.