The effect of Co substitution for Cu in Bi2Sr2Ca1Cu2O8−δ

Abstract We have grown single crystal whiskers of Bi 2 (SrCa) n +1 (Cu 1− x Co x ) n O 8− δ with 0 x R as a function of the temperature T . For x n =2 in the majority of the sample and n =3 in a small part. For both phases, the changes in T c and in the extrapolated residual resistance due to Co substitution are the same for Co as it is for Zn and Ni, indicating that magnetic scattering is not important. For x ≈0.06, oxygenation can drive the sample from superconducting to insulating, indicating that both the scattering of the carriers and the number of carriers affect the superconducting–insulating transition. This occurs in samples in which the sheet resistance in a CuO plane is approximately h /(2 e ) 2 . For x >0.18, the samples are insulating and n =1.