Infrared Optical Studies of Yttrium BARIUM(2) (COPPER(1-X)M(X))(3) OXYGEN(7-DELTA) (m = Zinc, Nickel) High Transition Temperature Superconductors.

The infrared reflectances R(nu,T) are presented of rm YBa_2(Cu _{1-x}M_{x})_3O _{7-delta} films (M = Zn, Ni) for frequencies 50 cm^{-1 } < nu < 1000 cm^{-1} and temperatures T = 10K, 100K and 300K. The "best fit" conductivities, sigma_1(nu,10K), for both Zn and Ni-doped films show no clear evidence of superconductivity, i.e., the superconducting density of states is very gapless. This degree of gaplessness is consistent with the large penetration depths measured in the same films. It agrees with estimates based on the measured carrier scattering rate 1/tau(10K) and theories of d-wave superconductors. The carrier scattering rate 1/tau(T) increases with dopant concentration x and with T; it does not change rapidly just below T_{C} as in pure rm YBa_2Cu_3O_ {7-delta}. The plasma frequency omega_{P} = 8500cm^ {-1} +/- 500cm^{-1}, independent of dopant concentration and T, agrees with values obtained in pure rm YBa_2Cu _3O_{7-delta} films.