Magnetic excitations of Fe_{1 +y}Se_xTe_{1 −x}in magnetic and superconductive phases

Abstract

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.

The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

“…Additional evidence for short-range antiferromagnetic ordering was observed in other investigations. [70][71][72][73][74] The phase diagram of Ref. 72 shows the short-range ordering regime extending all the way to x = 0.45, overlapping the region of bulk superconductivity.…”

“…Such measurements can give information on the spin wave dispersion relations of the magnetic excitations associated with the diagonal double stripe static ordering at wave vector 73 The data indicated "a quasitwo-dimensional system with weak interactions along c." The measurements also demonstrated that the magnetic excitations persisted up to temperatures of at least 150 K. 73 At present there are no dispersion relations reported in either the long-range ordered or spin glass region for the spin wave excitations originating from the statically ordered diagonal double stripe structure with tetragonal in-plane wave vector Here we further discuss the normal state aspects of the spin excitations.…”

“…In a theoretical study, Fang et al explained the transition from commensurate to incommensurate ordering with increasing y in Fe 1+y Te using a local moment J 1a - is replaced by static short-range "spin-glass" order [68][69][70][71][72][73][74] with a well-defined but slightly incommensurate wave vector 1 2 − δ, 0, 1 2 r.l.u. with δ ∼ 0.05, that is thus similar to the long-range diagonal double stripe ordering wave vector that occurs for x < ∼ 0.1 and small y. Xu et al report that the short-range ordering becomes more twodimensional with increasing x.…”

“…73,224,309,314,[320][321][322][323][389][390][391][392][393][394] An early example of neutron spin resonance mode data is shown in the top panel of Fig. 75 for polycrystalline Ba 0.6 K 0.4 Fe 2 As 2 .…”

Magnetic-crystallographic phase diagram of the superconducting parent compound Fe1+xTe

“…[20][21][22] A central question concerning iron telluride is whether the effect from anionic substitution is either to suppress a structural distortion, or just remove interstitial iron from the lattice. Of course, another possibility is that both are necessary for superconductivity.…”