Abstract. We report on the quasi-particle dynamics of the charge/orbital ordered (COO) and ferromagnetic clusters in the optimally doped manganite, La_0.7Ca_0.3MnO₃ (LCMO) single crystal by time-resolved two-color pump–probe spectroscopy. Pump photons with energies of ~1.55 and ~0.21 eV were employed in our transient optical spectroscopy to investigate the percolative phase separation including the COO and ferromagnetic clusters from 4 to 480 K. At 1.55 eV, the transient reflectivity change, ΔR/R, at Δt=0 shows a similar temperature dependence as that in resistivity and in neutron scattering intensity. We attribute the reflectivity signal to the characteristic optical response of the COO domains. We identify a new temperature scale T^*~400 K for the clean limit to the formation of COO clusters in LCMO. In contrast, the temperature-dependent amplitude of the transient reflectivity change in the mid-infrared (IR) absorption band (~5 μm) scales with the volume fraction of the ferromagnetic metallic (FM) phases. Our results suggest ultrafast optical spectroscopy to be a powerful probe to reveal the correlated polarons and charge disorders in phase-separated manganites.

Received 19 July 2009
Published 6 November 2009