Magnetic excitations of Fe1 + ySexTe1 - X in magnetic and superconductive phases

Department of Physics, Clarendon Laboratory, Oxford University, Oxford OX1 3PU, UK.
Journal of Physics Condensed Matter (Impact Factor: 2.35). 04/2010; 22(14):142202. DOI: 10.1088/0953-8984/22/14/142202
Source: PubMed


We have used inelastic neutron scattering and muon-spin rotation to compare the low energy magnetic excitations in single crystals of superconducting Fe(1.01)Se(0.50)Te(0.50) and non-superconducting Fe(1.10)Se(0.25)Te(0.75). We confirm the existence of a spin resonance in the superconducting phase of Fe(1.01)Se(0.50)Te(0.50), at an energy of 7 meV and a wavevector of (1/2, 1/2, 0). The non-superconducting sample exhibits two incommensurate magnetic excitations at (1/2, 1/2, 0) ± (0.18, - 0.18, 0) which rise steeply in energy, but no resonance is observed at low energies. A strongly dispersive low energy magnetic excitation is also observed in Fe(1.10)Se(0.25)Te(0.75) close to the commensurate antiferromagnetic ordering wavevector (1/2 - δ, 0, 1/2), where δ≈0.03. The magnetic correlations in both samples are found to be quasi-two-dimensional in character and persist well above the magnetic (Fe(1.10)Se(0.25)Te(0.75)) and superconducting (Fe(1.01)Se(0.50)Te(0.50)) transition temperatures.

Download full-text


Available from: Ekaterina Pomjakushina, Jul 10, 2014
  • Source
    • "Data in (b) was measured for k < 0 and then symmetrized with respect to k = 0. (c), (d) show fits of the corresponding data on the left to the model of a mixture of UDUD plaquettes, (e), prevailing at low temperature , and the UUUU (FM) plaquettes, (f), emergent on warming. spin resonance, were observed by different groups in various FeTe 1−x Se x samples, both with suppressed and welldeveloped superconductivity [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31]. In the absence of even a qualitative description, these results were often compared with ad-hoc functions, such as a Sato-Maki function, leading to data parameterizations void of much physical meaning [22]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We report neutron scattering measurements, which reveal spin-liquid polymorphism in a '11' iron chalcogenide superconductor, a poorly-metallic magnetic FeTe tuned towards superconductivity by substitution of a small amount of Tellurium with iso-electronic Sulphur. We observe liquid-like magnetic dynamics, which is described by a competition of two phases with different local structure, whose relative abundance depends on temperature. One is the ferromagnetic (FM) plaquette phase observed in the non-superconducting FeTe, which preserves the C$_4$ symmetry of the underlying square lattice and is favored at high temperatures. The other is the antiferromagnetic plaquette phase with broken C$_4$ symmetry, which emerges with doping and is predominant at low temperatures. These findings suggest a first-order liquid-liquid phase transition in the electronic spin system of FeTe$_{1-x}$(S,Se)$_x$. We thus discover remarkable new physics of competing spin liquid polymorphs in a correlated electron system approaching superconductivity. Our results facilitate an understanding of large swaths of recent experimental data in unconventional superconductors.
    Proceedings of the National Academy of Sciences 02/2015; 112(33). DOI:10.1073/pnas.1503559112 · 9.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The response of the worldwide scientific community to the discovery in 2008 of superconductivity at Tc = 26 K in the Fe-based compound LaFeAsO_{1-x}F_x has been very enthusiastic. In short order, other Fe-based superconductors with the same or related crystal structures were discovered with Tc up to 56 K. Many experiments were carried out and theories formulated to try to understand the basic properties of these new materials and the mechanism for Tc. In this selective critical review of the experimental literature, we distill some of this extensive body of work, and discuss relationships between different types of experiments on these materials with reference to theoretical concepts and models. The experimental normal-state properties are emphasized, and within these the electronic and magnetic properties because of the likelihood of an electronic/magnetic mechanism for superconductivity in these materials. Comment: 148 two-column typeset pages, including 96 figures, 35 tables and 583 references; pdf: 8.0 MB; v2: significantly enhanced and expanded; accepted for publication in Advances in Physics
    Advances In Physics 05/2010; 59(6). DOI:10.1080/00018732.2010.513480 · 20.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Isoelectronic Tellurium (Te) substitution for Selenium (Se) in the tetragonal phase of FeSe (β-FeSe) increases the superconducting transition temperature (Tc) by applying a negative pressure on the lattice. However, the normal state resistivity increases and shows semi-metallic behavior for samples with higher Te concentration. With increasing Te concentration, the Tc increases and reaches a maximum for FeSe0.5Te0.5 and then decreases with further increase of Te. We have investigated the effect of Cobalt (Co) and Nickel (Ni) doping in FeSe0.5Te0.5 in the nominal composition range Fe1−xTMxSe0.5Te0.5 (TM = Co (x = 0.05, 0.1, 0.15, 0.2) and Ni (x = 0.05, 0.1)). Both Co and Ni doping suppress Tc and drives the system to metal–insulator transition. The in-plane (‘a’) and out-of-plane (‘c’) lattice constants decrease with increasing dopant concentration.
    Physica C Superconductivity 07/2010; 470(13-14):528-532. DOI:10.1016/j.physc.2010.04.009 · 0.94 Impact Factor
Show more