Suppression of the <i>s</i>-Wave Order Parameter Near the Surface of the Infinite-Layer Electron-Doped Cuprate Superconductor Sr_0.9La_0.1CuO₂

Abstract

The temperature dependencies of the in-plane (λab) and out-of-plane (λc) components of the magnetic field penetration depth were investigated near the surface and in the bulk of the electron-doped superconductor Sr0.9La0.1CuO2 by means of magnetization measurements. The measured λab(T) and λc(T) were analyzed in terms of a two-gap model with mixed s+d-wave symmetry of the order parameter. λab(T) is well described by an almost pure anisotropic d-wave symmetry component (≃96%), mainly reflecting the surface properties of the sample. In contrast, λc(T) exhibits a mixed s+d-wave order parameter with a substantial s-wave component of more than 50%. The comparison of λab−2(T) measured near the surface with that determined in the bulk by means of the muon-spin rotation/relaxation technique demonstrates that the suppression of the s-wave component of the order parameter near the surface is associated with a reduction of the superfluid density by more than a factor of two.

Keywords

• superconductivity
• cuprates
• magnetic penetration depth
• order parameter
• superconducting gap structure