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

Nature Physics (Impact Factor: 19.35). 07/2009; DOI:10.1038/nphys1512
Source: OAI

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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    ABSTRACT: Cuprates, ferropnictides and ferrochalcogenides are three classes of unconventional high temperature superconductors, who share similar phase diagrams in which superconductivity develops after a magnetic order is suppressed, suggesting a strong interplay between superconductivity and magnetism, although the exact picture of this interplay remains elusive. Here we show that there is a direct bridge connecting antiferromagnetic exchange interactions determined in the parent compounds of these materials to the superconducting gap functions observed in the corresponding superconducting materials: in all high temperature superconductors, the Fermi surface topology matches the form factor of the pairing symmetry favored by local magnetic exchange interactions. We suggest that this match offers a principle guide to search for new high temperature superconductors.
    Scientific Reports 01/2012; 2:381. · 2.93 Impact Factor
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    ABSTRACT: The Fe1+yTe1-xSex series of materials is one of the prototype families of Fe-based superconductors. To provide further insight into these materials we present systematic inelastic neutron scattering measurements of the low energy spin excitations for x=0.27, 0.36, 0.40, 0.49. These measurements show an evolution of incommensurate spin excitations towards the (1/2 1/2 0) wave vector with doping. Concentrations (x=0.40 and 0.49) which exhibit the most robust superconducting properties have spin excitations closest to (1/2 1/2 0) and also exhibit a strong spin resonance in the spin excitation spectrum below Tc. The resonance signal appears to be closer to (1/2 1/2 0) than the underlying spin excitations. We discuss the possible relationship between superconductivity and spin excitations at the (1/2 1/2 0) wave vector and the role that interstitial Fe may play.
    Physical review. B, Condensed matter 05/2013; 87(22).
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    ABSTRACT: The emergence of nematic electronic states which break the symmetry of the underlying lattice is a recurring theme in many correlated electron materials, among them the high temperature copper-oxide and iron-based superconductors. In both cuprate and iron-based superconductors, the symmetry breaking states emerge on the underdoped side of the phase diagram, where the superconductivity is suppressed and the transition to a magnetically ordered phase (or the pseudogap phase in the cuprates) takes place. Nematic electronic states have also been detected in systems which have a quantum critical point, indicating an intimate relationship between electronic correlations and nematic ordering. Here we provide evidence for the existence of nematic electronic states in the iron chalcogenide superconductor FeSe0.4Te0.6. The symmetry breaking states persist above Tc into the normal state. We compare our results with the quasiparticle interference patterns obtained within a tight-binding model, accounting for orbital ordering. The amplitude of the nematic excitations is found to anticorrelate with the local gap size, indicating a competition between the two.

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