Abrupt changes in electronic relaxation and lattice dynamics across the structural phase transition in lightly doped Ca$_{2}$RuO$_{4}$ observed via time-resolved optical reflectivity

Ca$_{2}$RuO$_{4}$ is a multiband strongly correlated electron system that undergoes a structural phase transition at Ts ~ 360K that is concomitant with an insulator-to-metal transition and a rearrangement of orbital occupancy. Understanding its structural and electronic response to ultrafast optical excitation can provide insight about the microscopic mechanism of this phase transition.We report temperature and fluence dependent time resolved optical reflectivity measurements from lightly doped Ca$_{2}$RuO$_{4}$ single crystals. Abrupt changes in both the electronic relaxation dynamics and multiple lattice vibrational modes are observed, including the softening of two optical phonon modes as Ts is approached. We will discuss the relevance of our results to existing theories of the mechanism underlying the structural phase transition in Ca$_{2}$RuO$_{4}$ as well as the possibility of photo-inducing this phase transition on ultrafast time scales.