Effect of magnetic field on the superconducting phase in the electron-doped metallic double-chain compound Pr₂Ba₄Cu₇O _15-δ

We report the magnetotransport and dc magnetic susceptibility of the polycrystalline samples of Pr₂Ba₄Cu₇O _15-δ, to examine the effect of magnetic field on the superconducting phase of the metallic CuO double-chain. The resistive critical magnetic field is estimated to be about 21 T at low temperatures from the resistive transition data. On the other hand, the corresponding critical field determined from the magnetization measurements gives rise to a very low value of ̃0.3 T at 2 K. These discrepancies in the magnetic response between the resistivity and magnetization data are caused by disappearance of the magnetically shielding effect even in relatively lower fields. In spite of the observation of the resistive drop associated with the superconducting transport currents, the suppression of the diamagnetic signal is probably related to the superconductivity of quasi one-dimensional CuO double-chain. The behavior of Seebeck coefficient in the superconducting Pr₂Ba₄Cu ₇O_15-δ is discussed on the basis of the double chain model from the density functional band calculation.