Monday, July 16, 2012, 1:30 pm — Small Seminar Room, Bldg. 510
Newly discovered alkali-metal intercalated FeSe superconductor has a maximum transition temperature of ~31K. About thirteen Raman phonon modes are observed in the new superconductor, much larger than that expected for an ideal BaFe2As2-like structure. We deduce possible forms of Fe-vacancy ordering by careful analysis of polarization and crystal rotations. Most of the Raman modes can be well assigned in combination of first-principles calculations. We further investigate the effect of alkali-metal and Fe substitution on Raman modes. Two-magnon peak is also observed around 200meV in AFe1.6Se2. Interestingly, the intensity of the two-magnon peak falls sharply on entering the superconducting phase, while this effect is completely absent in non-superconducting KFe1.5Fe2. This reveals a strong competition between antiferromagnetism and superconductivity, which may arise from the proximity effect within regions of microscale phase separation.
Hosted by: Genda Gu
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