Title: PHONON DENSITY OF STATES OF SUPERCONDUCTING IRON SELENIDE
D. Phelan1, J. N. Millican1, E. L. Thomas2, J. B. Leao1, Y. Qiu1,3, and R. Paul1
Mentor: Peter Gehring1
1NIST Center for Neutron Research, NIST Gaithersburg, MD 20899.
2Ceramics Division, NIST Gaithersburg, MD 20899.
3Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742.
In 2008, superconductivity with high Tc (up to 56 K) was reported in a number of Fe containing materials, and a vigorous search for the origin of this behaviour is being conducted worldwide. Almost all of these materials have contained both Fe and As - the exception being the Fe(Te/Se/S)1-x binary series . Thus the study of this unique series is useful in that it might help to identify some universal feature of Fe-based superconductors or, on the other hand, it might serve to show that there are differing mechanisms of superconductivity in the compounds. In fact, the series is interesting in its own right due to the possibility of a relation of magnetism of the Fe atoms to the superconductivity and, additionally, the observation that Tc is significantly enhanced by applied pressure .
In a conventional superconductor, superconductivity is mediated by phonons. For the case of FeSe, recent density functional calculations showed that standard electron-phonon coupling theory could not come close to accounting for such a high transition temperature . To test these calculations, we synthesized polycrystalline FeSe (Tc ~ 8 K) and carried out inelastic neutron scattering measurements of the phonon density of states. These measurements generally support the calculations and show that the spectral weight of lattice vibrations is too low to account for the superconducting properties.
 F. –C. Hsu et al., Proc. Natl. Acad. Sci. U.S.A. 105, 14262, (2008)
 Y. Mizuguchi et al., Appl. Phys. Lett. 93, 152505, (2008)
 A. Subedi et al., Phys. Rev. B 78, 134514, (2008)
Name Daniel Phelan
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Building 235, Room A113, Stop 6102
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Mentors Name: Peter Gehring, email: firstname.lastname@example.org, Tel.: (301) 975-3946
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