Broadband THz spectroscopy of the insulator-metal transition driven by coherent lattice deformation at the SmNiO3/LaAlO3 interface

TL;DR

This study uses broadband THz spectroscopy to explore how coherent lattice deformation at the SmNiO3/LaAlO3 interface induces a non-equilibrium insulator-metal transition, revealing the transition's dynamics and underlying mechanisms.

Contribution

It demonstrates that the insulator-metal transition is driven by interface charge rearrangement rather than magnetic order melting, using broadband THz spectroscopy to analyze transient optical properties.

Findings

The metallic phase has the same carrier density as the equilibrium phase.

The LaAlO3 substrate acts as a transducer only at early times, with no long-term structural change.

The transition occurs both below and above the Néel temperature, independent of magnetic order.

Abstract

We investigate the non-equilibrium 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 transition may origin from the rearrangement of ordered charges at the interface propagating into the film.