Publication Date:
2016-07-08
Description:
We report Raman light scattering in the phase separated superconducting single crystal Rb 0.77 Fe 1.61 Se 2 with T c = 32 K over a wide temperature region 3–500 K. The observed phonon lines from the majority vacancy ordered Rb 2 Fe 4 Se 5 (245) antiferromagnetic phase with T N = 525 K demonstrate modest anomalies in the frequency, intensity and halfwidth at the superconductive phase transition. We identify phonon lines from the minority compressed Rb δ Fe 2 Se 2 (122) conductive phase. The superconducting gap with d x 2 − y 2 symmetry has been detected in our spectra. In the range 0–600 cm −1 we observe a weak but highly polarized B 1 g -type background which becomes well-structured upon cooling. A possible magnetic or multiorbital origin of this background is discussed. We argue that the phase separation in M 0.8+ x Fe 1 . 6+y Se 2 is of pure magnetic origin. It occurs below the Néel temperature when the magnetic moment of iron reaches a critical value. We state that there is a spacer between the majority 245 and minority 122 phases. Using ab initio spin-polarized band structure calculations we demonstrate that the compressed vacancy ordered Rb 2 Fe 4 Se 5 phase can be conductive and therefore may serve as a protective interface spacer between the purely metallic Rb δ Fe 2 Se 2 phase and the insulating Rb 2 Fe 4 Se 5 phase providing percolative Josephson-junction like superconductivity all throughout of Rb 0.8+ x Fe 1.6+ y Se 2 . Our lattice dynamics calculations show significant differences in the phonon spectra of the conductive and insulating Rb 2 Fe 4 Se 5 phases.
Print ISSN:
1063-777X
Electronic ISSN:
1090-6517
Topics:
Physics
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