Optically Driven Dynamics of a Mott Insulator‐to‐Metal Transition

Abstract

Fundamental understanding and on‐demand control of correlation‐driven insulator‐to‐metal transitions (IMTs) via nonequilibrium drive are prime targets of current materials research, especially in view of a host of potential applications in a wide range of next‐generation quantum devices. Photoinduced switching between competing orders in correlated insulators requires a free‐energy landscape with nearly degenerate ground states, which is commonly reached in 3d‐electron materials through heavy doping, strain, or the application of static electric fields. The associated spatial inhomogeneity leads to a photoinduced phase transition (PIPT) that remains confined near the illuminated region. Here, optical spectroscopy experiments are reported within the hysteretic region at the first‐order IMT in the 4d‐electron compound Ca3(Ru0.99Ti0.01)2O7 and show that specific Ru interband transitions resonantly excited by light with a threshold fluence corresponding to the planar density of Ru atoms can trigger reversible, avalanche‐like coherent propagation of phase interfaces across the full extent of a macroscopic sample, in the absence of assisting external stimuli. Based on detailed comparison of spectroscopic data to density functional calculations, we attribute the extraordinary photo‐sensitivity of the IMT to an exceptionally shallow free‐energy landscape generated by the confluence of electron–electron and electron‐lattice interactions. These findings highlight Ca3(Ru0.99Ti0.01)2O7 as a powerful model system for building and testing a theory of Mott transition dynamics in the presence of strong electron‐lattice coupling and may pave the way toward nanoscale devices with quantum‐level photosensitivity.