Superconducting state coexisting with a phase-separated static magnetic order in(Ba,K)Fe2As2,(Sr,Na)Fe2As2, andCaFe2As2Journal Articles
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abstract
The recent discovery and subsequent developments of FeAs-based
superconductors have presented novel challenges and opportunities in the quest
for superconducting mechanisms in correlated-electron systems. Central issues
of ongoing studies include interplay between superconductivity and magnetism as
well as the nature of the pairing symmetry reflected in the superconducting
energy gap. In the cuprate and RE(O,F)FeAs (RE = rare earth) systems, the
superconducting phase appears without being accompanied by static magnetic
order, except for narrow phase-separated regions at the border of phase
boundaries. By muon spin relaxation measurements on single crystal specimens,
here we show that superconductivity in the AFe$_{2}$As$_{2}$ (A = Ca,Ba,Sr)
systems, in both the cases of composition and pressure tunings, coexists with a
strong static magnetic order in a partial volume fraction. The superfluid
response from the remaining paramagnetic volume fraction of
(Ba$_{0.5}$K$_{0.5}$)Fe$_{2}$As$_{2}$ exhibits a nearly linear variation in T
at low temperatures, suggesting an anisotropic energy gap with line nodes
and/or multi-gap effects.
