Article

# Evolution of spin excitations into the superconducting state in FeTe1-xSex

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(Impact Factor: 20.15). 07/2009; 6(3). DOI: 10.1038/nphys1512
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ABSTRACT

The origin of the superconducting state in the recently discovered Fe-based materials is the subject of intense scrutiny. Neutron scattering and NMR measurements have already demonstrated a strong correlation between magnetism and superconductivity. A central unanswered question concerns the nature of the normal-state spin fluctuations that may be responsible for the pairing. Here we present inelastic neutron scattering measurements from large single crystals of superconducting and non-superconducting Fe1+yTe1-xSex. These measurements indicate a spin fluctuation spectrum dominated by two-dimensional incommensurate excitations extending to energies greater than 250;meV. Most importantly, the spin excitations in Fe1+yTe1-xSex have four-fold symmetry about the (1, 0) wavevector (square-lattice (pi,pi) point). Moreover, the excitations are described by the identical wavevector and can be characterized by the same model as the normal-state spin excitations in the high-TC cuprates. These results demonstrate commonality between the magnetism in these classes of materials, which perhaps extends to a common origin for superconductivity.

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• "One of the consequences of this superconducting state is that the imaginary part of the dynamic susceptibility, χ ′′ (Q, ω) should have a sharp peak, termed spin resonance in copper oxide superconductors [26], at Q AF = (1, 0) below T c [27] [28]. This prediction is also confirmed by inelastic neutron scattering (INS) experiments in iron-based superconductors such as hole-doped Ba 1−x K x Fe 2 As 2 [29] [30] [31], electron-doped BaFe 2−x T x As 2 (T =Co, Ni) [32] [33] [34] [35] [36] [37] [38], and FeTe 1−x Se x [39] [40] [41]. Finally, angle resolved photoemission spectroscopy (ARPES) experiments find that the general characterization of the FS and the superconducting order parameter are consistent with the band structure calculations and with isotropic s-wave superconducting gaps [42]. "
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