Hall coefficients and optical properties of La/sub 2-//sub x/Sr/sub x/CuO4 single-crystal thin films

The low-field Hall coefficient R/sub H/, optical reflectance and transmittance of the La/sub 2-//sub x/Sr/sub x/CuO4 system with various Sr concentrations from x = 0 to 0.36 are systematically studied using single-crystal thin films epitaxially grown on (100) face SrTiO3 substrates with the c axis normal to the film surface. For the x range measured, R/sub H/ is positive and decreases more rapidly than that expected from the Sr concentration but more slowly than reported earlier for polycrystalline specimens, indicating anisotropy of R/sub H/. Furthermore, the x dependence indicates deviation from that expected from a simple band model. Within the superconducting composition range, R/sub H/ exhibits characteristic temperature dependence. The optical reflectance spectrum changes from that of a semiconductor at x = 0 to a typical metallic one characterized by the Drude model for x>0.1, indicating the development of itinerant holes in the Cu-O planes. In the optical transmission spectra, an anomalous absorption band is seen in addition to the fundamental absorption corresponding to an energy gap of about 2 eV. This band, which develops with Sr doping, implies an enhancement of the density of states near the Fermi level. Taking these observations into account, the normal-state transport properties are explained with a qualitative consistence