Broadband Terahertz Spectroscopy of the Insulator-Metal Transition Driven by Coherent Lattice Deformation at the $\mathrm{SmNiO_3/LaAlO_3}$ Interface

We investigate the nonequilibrium insulator-metal transition driven in a SmNiO3 thin film by coherent optical excitation of the LaAlO3 substrate lattice. By probing the transient optical properties over a broad frequency range (100−800 cm−1), we analyze both the time-dependent metallic plasma and the infrared optical phonon line shapes.We show that the light-induced metallic phase in SmNiO3 has the same carrier density as the equilibrium metallic phase. We also report that the LaAlO3 substrate acts as a transducer only at the earlier time delays, as the vibrations are driven coherently. No long-lived structural rearrangement takes place in the substrate. Finally, we show that the transient insulator-metal transition occurs both below and above the N´eel temperature. We conclude that the supersonic melting of magnetic order measured with ultrafast x rays is not the driving force of the formation of the metallic phase.We posit that the insulator-metal transitionmay origin from the rearrangement of ordered charges at the interface propagating into the film