Gate-tunable THz emission at oxide interfaces via ultrafast spin-to-charge current conversion*

Two-dimensional electron systems at oxide interfaces such as LaAlO₃ / SrTiO₃ provide promising platforms for achieving fast, tunable, and efficient spin-charge inter-conversion. Here, we report gate-tunable, ultrafast spin-to-charge current conversion in NiFe / LaAlO₃ / SrTiO₃, measured by THz emission spectroscopy. Upon ultrafast laser excitation, we found the sign of the emitted single-cycle THz pulses follows the direction of the magnetization in NiFe, and its magnitude decreases with increasing the thickness of the LaAlO₃ layer. These findings support that the spin-charge conversion occurs at the LaAlO₃ / SrTiO₃ interface. Furthermore, we demonstrate that the amplitude of the emitted THz pulses can be tuned by electrostatic gating. Our findings extend ultrafast spin-charge conversion to oxides-based systems, thus providing a crucial link between ultrafast spintronics and correlated phenomena in complex oxides.