Ultrafast dynamics in the Lifshitz-type 5$d$ pyrochlore antiferromagnet Cd${}_2$Os${}_2$O${}_7$

Abstract

We investigate the ultrafast dynamics of Cd${}_2$Os${}_2$O${}_7$, a prototype material showing a Lifshitz-type transition as a function of temperature. In the paramagnetic metallic state, the photo-reflectivity shows a sub-picosecond relaxation, followed by a featureless small offset. In the antiferromagnetic state slightly below $T_N$, however, the photo-reflectivity resurges over hundreds of picoseconds, which goes beyond the usual realm of the effective-temperature model. Our observations are consistent with the Lifshitz phase transition of Cd${}_2$Os${}_2$O${}_7$ driven by the evolution of the local magnetic moment.

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