Ultrafast quasiparticle dynamics in correlated semimetals (Conference Presentation)

The correlated polar semimetal Ca3Ru2O7 exhibits a rich phase diagram including two magnetic transitions (TN =56 K and TC =48 K) with the appearance of an insulating-like pseudogap (at TC ). In addition, there is a crossover back to metallic behavior at T∗=30 K, the origin of which is still under debate. We utilized ultrafast optical pump optical probe spectroscopy to investigate quasi- particle dynamics as a function of temperature in this enigmatic quantum material. n conjunction with density functional theory, our experimental results synergistically reveal the origin of the T-dependent pseudogap. Further, our data and analysis indicate that the T∗ emerges as a natural consequence of T-dependent gapping out of carriers, and does not correspond to a separate electronic transition. Our results highlight the value of low fluence ultrafast optics as a sensitive probe of low energy electronic structure, thermodynamic parameters, and transport properties of Ruddlesden-Popper ruthenates.