Ultrafast Terahertz Field Control of the Emergent Magnetic and Electronic Interactions at Oxide Interfaces

Ultrafast electric-field control of emergent electronic and magnetic statesat oxide interfaces offers exciting prospects for the development of newgenerations of energy-efficient devices. Here, we demonstrate that theelectronic structure and emergent ferromagnetic interfacial state in epitaxialLaNiO3/CaMnO3 superlattices can be effectively controlled using intensesingle-cycle THz electric-field pulses. We employ a combination ofpolarization-dependent X-ray absorption spectroscopy with magnetic circulardichroism and X-ray resonant magnetic reflectivity to measure a detailedmagneto-optical profile and thickness of the ferromagnetic interfacial layer.Then, we use time-resolved and temperature-dependent magneto-optical Kerreffect, along with transient optical reflectivity and transmissivitymeasurements, to disentangle multiple correlated electronic and magneticprocesses driven by ultrafast high-field ( 1 MV/cm) THz pulses. These processesinclude an initial sub-picosecond electronic response, consistent withnon-equilibrium Joule heating; a rapid ( 270 fs) demagnetization of theferromagnetic interfacial layer, driven by THz-field-induced nonequilibriumspin-polarized currents; and subsequent multi-picosecond dynamics, possiblyindicative of a change in the magnetic state of the superlattice due to thetransfer of spin angular momentum to the lattice. Our findings shed light onthe intricate interplay of electronic and magnetic phenomena in this stronglycorrelated material system, suggesting a promising avenue for efficient controlof two-dimensional ferromagnetic states at oxide interfaces using ultrafastelectric-field pulses.