Low energy dynamics in charge ordered R_0.5Sr_0.5MnO₃ (R = Nd and Pr) manganite thin films

The half-doped Pr_0.5Sr_0.5MnO₃ manganite represents a unique stripe type CO-orbital order that induces transport and magnetic anisotropy whereas the CO in Nd_0.5Sr_0.5MnO₃ is charge-exchange (CE)-type which is isotropic in nature. We have systematically explored epitaxial manganite thin films grown on (100), (110), and (111) oriented (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 substrates by pulsed laser deposition technique. Our Terahertz time-domain spectroscopic data reveal charge density wave (CDW) resonance centered around 5-6 meV for (110) oriented films and Drude-like conductivity for (100) and (111) oriented films. The CDW resonance in the optical conductivity spectra can be tuned from 4 meV to 6 meV for (110) oriented films and depends on the amount of ferromagnetic phase fraction in the CO matrix and corroborates well with the magnetization measurements. The nonlinear conductivity related to the sliding of the pinned CDW character makes the studied systems promising candidates for ultrafast coherent control of charge transport by resonant THz pumping.