Terahertz emission from LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures pumped with femtosecond laser

Abstract

Since the discovery of the ultrafast demagnetization of the ferromagnetic metal, the spin degree of electrons is gradually used to generate terahertz radiation. The terahertz radiation generated by the inverse Rashba-Edelstein effect was confirmed first at the interface of Ag/Bi. However, the spin-to-charge conversion efficiency of the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface is one order of magnitude lager than that of the Ag/Bi interface under equilibrium or quasi-equilibrium condition. Whether the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures can be used to convert spin current to generate terahertz radiation remains to be systemically studied. In this work, we fabricate the NiFe/LaAlO<sub>3</sub>//SrTiO<sub>3</sub> heterostructures and investigate the generation of terahertz radiation by femtosecond laser pumping and its dependence of the magnetic field direction. We change the thickness of the LaAlO<sub>3</sub> to show the applicability of the superdiffusive spin transport model and optical transmission model. We find the multireflections at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface weaken the terahertz radiation intensity. This work provides experimental and theoretical support for further optimizing the generation of terahertz electromagnetic waves.