Mid-and Near-IR Pump-Probe Study of Quasiparticle Dynamics in Ca₃Ru₂O₇

We have investigated near-IR reflectivity dynamics of single crystals of the Ruddlesden-Popper ruthenate Ca₃Ru₂O₇ using both near and mid infrared excitation. This correlated semimetal exhibits a pseudogap (~10meV) at T_c=48K, which coincides with an upturn in resistivity followed by a return to metallic behavior at 30K. Low-fluence pump-probe measurements have been able to establish the signatures of the pseudogap in both the rise-time and decay time of the near-IR reflectivity dynamics due to a phonon bottleneck [1]. Here measurements as a function of temperature, fluence, and pump wavelength show dynamics that indicate a possible photoinduced phase transition by comparison with pump-heating calculations and a fluence dependent rise-time that lasts up 20 picoseconds. Comparison with dynamics initiated with mid-infrared pump pulses do not indicate the excitation of coherent phonons as a large contributor to the observed response.

[1] Y. Yuan et al., “Ultrafast quasiparticle dynamics in the correlated semimetal Ca₃Ru₂O₇,” Phys. Rev. B 99, 155111 (2019)