Infrared study of superconductivity in YBa2(Cu1−xMx)3O7−δ (M=Zn and Ni)

Abstract

We report the infrared reflectances R(ν,T) of YBa2(Cu1−xMx)3O7−δ films (M=Zn and Ni) for frequencies 50 cm−1<ν<1000 cm−1 and temperatures T=10, 100, and 300 K. The ‘‘best fit’’ conductivities, σ1(ν,10 K), 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/τ (10 K) and theories of d-wave superconductors. The carrier scattering rate 1/τ(T) increases with dopant concentration x and with T; it does not change rapidly just below Tc as in pure YBa2Cu3O7−δ. The plasma frequency ωp=8500±500 cm−1, independent of dopant concentration and T, agrees with values obtained in pure YBa2Cu3O7−δ.

Source-reported materials — not catalogue approval

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