Precise and ultrafast control over photo-induced charge currents across nanoscale interfaces could lead to important applications in energy harvesting, ultrafast electronics, and coherent terahertz sources. Recent studies have shown that several relativistic mechanisms, including inverse spin-Hall effect, inverse Rashba–Edelstein effect, and inverse spin-orbit-torque effect, can convert longitudinally injected spin-polarized currents from magnetic materials to transverse charge currents, thereby harnessing these currents for terahertz generation. However, these mechanisms typically require external magnetic fields and exhibit limitations in terms of spin-polarization rates and efficiencies of relativistic spin-to-charge conversion. We present a nonrelativistic and nonmagnetic mechanism that directly utilizes the photoexcited high-density charge currents across the interface. We demonstrate that the electrical anisotropy of conductive oxides RuO2 and IrO2 can effectively deflect injected charge currents to the transverse direction, resulting in efficient and broadband terahertz radiation. Importantly, this mechanism has the potential to offer much higher conversion efficiency compared to previous methods, as conductive materials with large electrical anisotropy are readily available, whereas further increasing the spin-Hall angle of heavy-metal materials would be challenging. Our findings offer exciting possibilities for directly utilizing these photoexcited high-density currents across metallic interfaces for ultrafast electronics and terahertz spectroscopy.
Manipulation of a spin current at nanoscale is desired in many proposed spintronics devices. Magnetic multilayers consisting of ferromagnetic, ferrimagnetic and nonmagetic materials show rich phenomena when a spin current propagates through the multilayers. An interface of ferromagnetic and nonmagnetic metals has been demonstrated to play an important role in the generation and dissipation of a spin current. Using first-principles scattering calculation, we study the transport and relaxation of spin currents in typical transition metals and alloys and their interfaces. In particular, we focus on identifying the correlation of spin transport and relaxation with the specific order parameters of magnetic materials. By examining the spin-Hall conductivity and spin-flip diffusion length as a function of conductivity (resistivity), we are able to distinguish different dominant physical mechanisms of the generation and dissipation of spin currents.
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