Optical probe of anisotropic and incoherent charge dynamics in a layered ferromagnet

Highly anisotropic optical conductivity spectra and their temperature variation have been investigated for a layered ferromagnetic (Formula presented)=121 K) crystal of La(Formula presented)Sr(Formula presented)Mn(Formula presented)O(Formula presented)=0.4). The in-plane spectra show conspicuous spectral-weight transfer over an energy region of 0-3 eV with evolution of spin polarization below (Formula presented) and in the ferromagnetic, highly conducting ground state form a prominent peak structure around 0.4 eV with minimal Drude weight. By contrast, the (Formula presented)-axis spectra show little change with temperature and remain insulatorlike. The results indicate highly incoherent dynamics of the fully quasi-two dimensional spin-polarized carriers.