Ultrafast Generation of Spin Polarization in an Organic / 2D Heterostructure*

The ability to generate spin polarization and spin current on femtosecond time-scales is of vital importance for spintronics, quantum information science and novel spin-based low-energy electronics modalities. Current approaches relying on superdiffusive spin-transport in ferromagnetic structures are however limiting due to the need for external magnetic fields. Here we show instead by time-, spin- and angle-resolved photoemission that the combination of C₆₀ and WSe₂, two diamagnetic materials, create a 2D heterostructure that upon ultrafast excitation generates transient spin polarization without the need for an external magnetic field or ferromagnets. Optical excitation drives electron-transfer from C₆₀ to WSe₂ in a few hundred fs, and the charge-separation is accompanied by the build-up of a layer-dependent electric field across the heterointerface. This electric field induces a time- and layer-dependent Stark shift of the energy levels and valence bands at the interface, which due to spin-valley-layer locking in WSe₂ results in a transient spin polarization. This constitutes a new path for ultrafast spin manipulation without the need for external magnetic fields and may pave the way to ultrafast generation of spin currents.