paper

Direct observation of nanoscale interface phase in the superconducting chalcogenide K $_{x}$ Fe $_{2 - y}$ Se $_{2}$ with intrinsic phase separation

arXiv:1501.06745 · doi:10.1103/PhysRevB.91.020503

Abstract

We have used scanning micro x-ray diffraction to characterize different phases in superconducting K $_{x}$ Fe $_{2 - y}$ Se $_{2}$ as a function of temperature, unveiling the thermal evolution across the superconducting transition temperature (T $_{c} \sim$ 32 K), phase separation temperature (T $_{p s} \sim$ 520 K) and iron-vacancy order temperature (T $_{v o} \sim$ 580 K). In addition to the iron-vacancy ordered tetragonal magnetic phase and orthorhombic metallic minority filamentary phase, we have found a clear evidence of the interface phase with tetragonal symmetry. The metallic phase is surrounded by this interface phase below $\sim$ 300 K, and is embedded in the insulating texture. The spatial distribution of coexisting phases as a function of temperature provides a clear evidence of the formation of protected metallic percolative paths in the majority texture with large magnetic moment, required for the electronic coherence for the superconductivity. Furthermore, a clear reorganization of iron-vacancy order around the T $_{p s}$ and T $_{c}$ is found with the interface phase being mostly associated with a different iron-vacancy configuration, that may be important for protecting the percolative superconductivity in K $_{x}$ Fe $_{2 - y}$ Se $_{2}$ .

6 pages, 4 figures

Direct observation of nanoscale interface phase in the superconducting chalcogenide Kx​Fe2−y​Se2​ with intrinsic phase separation

Abstract

Direct observation of nanoscale interface phase in the superconducting chalcogenide K $_{x}$ Fe $_{2 - y}$ Se $_{2}$ with intrinsic phase separation