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SNS shows novel spin waves in iron chalcogenide Fe1.05Te


Fig. 1. (a)–(h): Constant energy slices of the data collected at vari- ous representa- tive energies. (a)-(c) collected on ARCS and (d)-(h) on MAPS.

Measurements conducted at the Spallation Neutron Source at ORNL have determined exchange couplings in the mag- netically ordered chalcogenide Fe1.05Te, a nonsuperconducting member of the iron-based family of superconductors. The results show the exchange pairings thought to be related to superconductivity occur in a next-nearest-neighbor ordering of atoms, rather than in nearest-neighbor order as in a previously studied iron arsenide.

Researchers from the University of Tennessee, ORNL, and other institutions collaborated to study the spin waves in Fe1.05Te. Superconductivity in iron-based superconductors emerges in proximity to magnetic order; similarly, many researchers think superconductivity in the copper oxides is driven by magnetic fluctuations. The magnetic order in Fe1.05Te is considerably different from the related iron pnictide superconducting system, raising the question of whether magnetism can in both cases still drive the superconductivity in iron-based superconductors.

To answer that question, the exchange coupling energies in the Fe1.05Te system were charac- terized using the ARCS instrument at SNS and other instruments to measure the spin waves (Fig. 1) and fitting the waves to a Heisenburg Hamiltonian. The dispersion of the spin waves in this sys- tem is novel and very different from that in the previously measured iron pnictide CaFe2As2. Fitted exchange couplings of J1a =-17.5 ± 5.7, J1b = -51.0 ± 3.4, J2 = J2a ≈ J2b = 21.7 ± 3.5, J3 = 6.8 ± 2.8 meV were found.

Although the nearest-neighbor couplings are very different (opposite in sign) from those in the pnictides, the next-nearest-neighbor couplings are isotropic and very similar. It has been shown theoretically that such an antiferromagnetic next-nearest-neighbor interaction can lead to the su- perconducting pairing symmetry observed in these systems. Therefore, the discovery of a universal next-nearest-neighbor coupling in these systems suggests superconductivity in both these classes of iron-based superconductors has a common magnetic origin that is intimately associated with the antiferromagnetic next-nearest-neighbor exchange couplings.

The paper was recently accepted for publication in Physical Review Letters.

“Spin waves in the (π, 0) magnetically ordered iron chalcogenide Fe1.05Te” by O. J. Lipscombe, G. F. Chen, C. Fang, T. G. Perring, D. L. Abernathy, A. D. Christianson, T. Egami, N. Wang, J. P. Hu, and P. Dai, Phys. Rev. Lett. (2011, in press)

Contact: Pengcheng Dai, 865-974-1509, daip@ornl.gov

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