Time-Resolved Optical Study Of The Ferroelectric Metal LiOsO₃

Recently, an inversion symmetry breaking metal-to-metal phase transition (T_c = 140K) was shown to exist in the strongly correlated spin-orbit coupled metal LiOsO₃, potentially realizing the long sought after ferroelectric metal first proposed by Anderson and Blount over a half century ago. However, the microscopic origin of the ferroelectric-like distortion below T_c remains unclear. In this work, ultrafast optical pump-probe spectroscopy experiments are utilized to address this question. We �find the fast carrier dynamics to display obvious signatures of the transition, with differing temperature dependence above and below T_c. A two-temperature model is developed to extract the electron-phonon coupling constant of LiOsO₃, which is found to be larger than previously thought. Our results provide critical insight into the dynamics of this uncommon phase transition.