Ultrafast Critical Dynamics of Ferroelectric Phase Transition in Pb${}_{1-x}$Ge${}_x$Te

Abstract

Transient responses of the electronic excitation and coherent soft phonon are investigated both above and below the ferroelectric phase transition temperature T${}_c$ in Pb${}_{1-x}$Ge${}_x$Te by using an optical pump-probe technique. The coherent soft mode shows large red-shift and heavily over-damped decay as the temperature approaching T${}_c$ from the low temperature side and the soft mode disappears above T${}_c$. The transient electronic response exhibits an abrupt change across T${}_c$. The critical behaviors of both the phononic and electronic dynamics are interpreted by the ferroelectric phase transition.

4 pages, 4 figures, corrected typos, accepted for publication in Physical Review B