Phase inhomogeneities in the charge-orbital-ordered manganite Nd_0.5Sr_0.5MnO₃ revealed through polaron dynamics

Ultrafast midinfrared spectroscopy is used to probe dynamics in the intermediate bandwidth manganite Nd0.5Sr0.5MnO3. In the majority paramagnetic and ferromagnetic phases, the early time dynamics are consistent with the excitation and subsequent redressing of uncorrelated lattice polarons, with longer time dynamics related to spin-lattice thermalization. These polaron excitations reveal the intrinsically inhomogeneous nature of these phases. At lower temperatures we observe ultrafast melting of charge-orbital order, liberating quasiparticles that subsequently relax into bound polaronic states on a subpicosecond time scale. The temperature-dependent amplitude of the polaron excitations scales with the volume fraction of the CE phase. Thus, polaron dynamics, as measured using ultrafast spectroscopy, serve as a sensitive probe of phase inhomogeneity.