Broadband Terahertz Spectroscopy Of The Insulator-Metal Transition Driven By Coherent Lattice Deformation At The Smnio3/Laalo3 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 Neel 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.