OPTICAL PROBE OF ANISOTROPIC AND INCOHERENT CHARGE DYNAMICS IN A LAYERED FERROMAGNET - LA1.2SR1.8MN2O7

Highly anisotropic optical conductivity spectra and their temperature variation have been investigated for a layered ferromagnetic (T-c=121 K) crystal of La2-2xSr1+2xMn2O7 (x=0.4). The in-plane spectra show con spicuous spectral-weight transfer over an energy region of 0-3 eV with evolution of spin polarization below T-c and in the ferromagnetic, hi ghly conducting ground state form a prominent peak structure around 0. 4 eV with minimal Drude weight. By contrast, the c-axis spectra show l ittle change with temperature and remain insulatorlike. The results in dicate highly incoherent dynamics of the fully quasi-two dimensional s pin-polarized carriers.