Ultrafast quasiparticle dynamics in correlated semimetal CaRuO
arXiv:1901.02512 · doi:10.1103/PhysRevB.99.155111
Abstract
The correlated polar semimetal CaRuO exhibits a rich phase diagram including two magnetic transitions (=56 K and =48 K) with the appearance of an insulating-like pseudogap (at ). In addition, there is a crossover back to metallic behavior at =30 K, the origin of which is still under debate. We utilized ultrafast optical pump optical probe spectroscopy to investigate quasiparticle dynamics as a function of temperature in this enigmatic quantum material. We identify two dynamical processes, both of which are influenced by the onset of the pseudogap. This includes electron-phonon relaxation and, below , the onset of a phonon bottleneck hindering the relaxation of quasiparticles across the pseudogap. We introduce a gap-modified two-temperature model to describe the temperature dependence of electron-phonon thermalization, and use the Rothwarf-Taylor to model the phonon bottleneck. In conjunction with density functional theory, our experimental results synergistically reveal the origin of the -dependent pseudogap. Further, our data and analysis indicate that emerges as a natural consequence of -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.
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