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.
Highlights
The order parameter in cuprate high-temperature superconductors (HTSs) is generally considered to be of pure d-wave symmetry
By applying an interacting boson-model used in nuclear physics theory to the D4h symmetry of HTSs, Iachello [25,26] demonstrated that a crossover from a d-wave order parameter symmetry at the surface to a d + s-wave symmetry in the bulk is possible from a group theoretical point of view
The temperature dependence of the magnetic penetration depth was extracted from the measured MAC by using the Shoenberg formula [36], modified for the known grain size distribution N(R) [37]: χ(T)
Summary
The order parameter in cuprate high-temperature superconductors (HTSs) is generally considered to be of pure d-wave symmetry. Experimental data obtained by using techniques that probe the bulk of the material, such as nuclear magnetic resonance [9], Raman scattering [10,11], neutron crystal-field spectroscopy [12,13,14], and muon-spin rotation/relaxation (μSR) [15,16,17] provide strong evidence for the presence of a substantial s-wave component in the order parameter Based on these experimental findings and on an earlier idea that in HTSs, two superconducting condensates with different order parameter symmetries (s- and d-wave) coexist [18,19,20], Müller [21,22,23,24] proposed a scenario in which the order parameter symmetry in HTSs changes from primarily d-wave at the surface to more d + s-wave in the bulk. The present results are compared with previous muon-spin rotation (μSR) experiments on Sr0.9La0.1CuO2 [34], which probe the magnetic penetration depth in the bulk of the sample
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