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

Abstract

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 60T. An anisotropy ratio of 8 was detected for the upper critical fields with H parallel (Hc2ab) and perpendicular (Hc2c) to the CuO2 planes, with Hc2ab extrapolating to near the Pauli paramagnetic limit of 160T. The longer superconducting coherence length than the lattice constant along the c axis indicates that the orbital degrees of freedom of the pairing wave function 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 of the magnetic field-temperature phase diagram between Hc2ab and the irreversibility line in the magnetization, Hirrab, in Sr0.9La0.1CuO2 is anomalously large for an electron-doped high-Tc cuprate. The large reversible region even approaching zero temperature rules out thermal depinning scenarios. The temperature dependence of Hirrab also differs fundamentally from those predicted for the quenched-disorder-induced vortex phase transitions for H‖c at low temperatures. Thus, our finding of a strongly suppressed Hirrab relative to Hc2ab at low temperatures is suggestive of the existence of additional quantum fluctuations, possibly due to a magnetic-field-induced competing order such as the spin-density wave (SDW).

Source-reported materials — not catalogue approval

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