Terahertz-Driven Ultrafast Dynamics of Rare-Earth Nickelates by Controlling Only the Charge Degree of Freedom

An important strategy for understanding the microscopic physics of strongly correlated systems and enhancing their technological potential is to selectively drive the fundamental degrees of freedom out of equilibrium. Intense terahertz (THz) pulses with photon energies of a few meV, can not only serve this purpose, but also unravel their electronic and quantum nature. Here, we demonstrate THz-driven ultrafast dynamics of rare-earth nickelates (RNiO₃, R = rare-earth atom) – a prototype system to study the Mott insulator-metal transition (IMT). The THz drive of the Mott insulating state induces instantaneous IMT via quantum tunneling of valence electrons across the bandgap while the THz drive of the correlated metallic state leads to overall heating of the conduction electrons. The subsequent relaxation of excited electrons in these two states occurs via a two-step process (electron-phonon thermalization and recovery of the charge-ordered insulating state) and a one-step process (electron-phonon scattering), respectively. The relaxation dynamics of the electrons and the absence of acoustic phonon modes, in particular, suggest a purely electronic and highly non-thermal nature of the THz-induced dynamics that is predominantly controlled by the charge degree of freedom. Such THz-induced IMT may find its applications in opto-electronics with enhanced performance and minimal device size and heat dissipation.