Terahertz Emission Spectroscopy to Probe Ultrafast Spin to Charge Conversion at Perovskite/Ferromagnet Interfaces

Understanding spin-to-charge conversion (SCC) allows efficient control and manipulation of the spin degree of freedom, which can pave the way for next generation spintronic devices. Unlike conventional transport-based measurements, terahertz (THz) emission spectroscopy offers great advantages including the capability of measuring transient charge currents with sub-picosecond time resolution. Using THz emission spectroscopy, we observed the ultrafast spin current injection at the interface between a ferromagnetic (FM) material and a chiral two-dimensional (2D) perovskite via inverse Rashba-Edelstein effect. In summary, we observed strong magnetic field- and polarization-dependence in both phase and intensity of the emitted THz signal, implying the great tunability in these chiral 2D perovskites for spintronic application. These results present a promising way to control charge and spin interconversion at perovskite/ferromagnetic interfaces and future spintronics devices. The unique asymmetry in THz emission due to SCC at chiral 2D perovskite/FM (i.e. (R-MBA)₂PbI₄/NiFe and (S-MBA)₂PbI₄) interface distinguishes them from three-dimensional perovskite materials which only exhibiit symmetric THz emission. In this talk, I will discuss the measured THz emission signals including both the forward and backward THz emission (reflected at the air/substrate interface). The forward emission signal exhibits a π-phase shift when the in-plane magnetic field flips its sign, whereas the backward signal exhibits no phase shift at all. In addition, I will also discuss the asymmetry in THz emission intensity. Specifically, the THz emission intensity of the forward emission signal decreases by almost two-fold when the in-plane magnetic field reverses, while the backward emission signal increases by two-fold when the field direction reverses. Such asymmetry in THz emission can be explained with an in-plane momentum shift of the Rashba bands induced by the ultrafast laser pump.