Dimensionality of superconductivity and vortex dynamics in the infinite-layer cuprate Sr0.9M0.1CuO2 (M=La,Gd) (original) (raw)

The high magnetic field phase diagram of the electron-doped infinite layer high-temperature superconducting (high-Tc) compound Sr0.9La0.1CuO2 was probed by means of penetration depth and magnetization measurements in pulsed fields to 60 T. An anisotropy ratio of 8 was detected for the upper critical fields with H parallel (H ab c2 ) and perpendicular (H c c2 ) to the CuO2 planes, with H ab c2 extrapolating to near the Pauli paramagnetic limit of 160 T. The longer superconducting coherence length than the lattice constant along the c-axis indicates that the orbital degrees of freedom of the pairing wavefunction are three dimensional. By contrast, low-field magnetization and specific heat measurements of Sr0.9Gd0.1CuO2 indicate a coexistence of bulk s-wave superconductivity with large moment Gd paramagnetism close to the CuO2 planes, suggesting a strong confinement of the spin degrees of freedom of the Cooper pair to the CuO2 planes. The region between H ab c2 and the irreversibility line in the magnetization, H ab irr , is anomalously large for an electron-doped high-Tc cuprate, suggesting the existence of additional quantum fluctuations perhaps due to a competing spin-density wave order.