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

TL;DR

This study investigates the anisotropic superconducting properties and dimensionality of electron-doped Sr0.9M0.1CuO2, revealing three-dimensional orbital pairing and confined spin degrees of freedom, with implications for understanding high-temperature superconductivity.

Contribution

It provides detailed measurements of critical fields, coherence lengths, and magnetic behavior, highlighting the three-dimensional nature of pairing and spin confinement in these cuprates.

Findings

Anisotropy ratio of 8 for critical fields.

Upper critical field near the Pauli limit.

Coexistence of s-wave superconductivity with Gd paramagnetism.

Abstract

The high magnetic field phase diagram of the electron-doped infinite layer high-temperature superconducting (high-T_c) compound Sr_{0.9}La_{0.1}CuO_2 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_{c2}^{ab}) and perpendicular (H_{c2}^c) to the CuO_2 planes, with H_{c2}^{ab} 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 Sr_{0.9}Gd_{0.1}CuO_2 indicate a coexistence of bulk s-wave superconductivity with large moment Gd paramagnetism close to the CuO_2 planes, suggesting a strong confinement of the spin degrees of freedom of the Cooper pair to the CuO_2 planes. The region between H_{c2}^{ab} and the irreversibility line in the magnetization, H_{irr}^{ab}, is anomalously large for an electron-doped high-T_c cuprate, suggesting the existence of additional quantum fluctuations perhaps due to a competing spin-density wave order.