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Anisotropic Spin Fluctuations in Detwinned FeSe



Tong Chen, Youzhe Chen, Andreas Kreisel, Xingye Lu, Astrid Schneidewind, Yiming Qiu, J. T. Park, Toby G. Perring, J. Ross Stewart, Huibo Cao, Rui Zhang, Yu Li, Yan Rong, Yuan Wei, Brian M. Andersen, P. J. Hirschfeld, Collin L. Broholm, Pengcheng Dai


Superconductivity in iron selenide (FeSe) emerges from a nematic phase that breaks four-fold rotational symmetry in the iron plane [Fig. 1(a)] [1-4]. Although this phase in FeSe is established below a tetragonal-to-orthorhombic transition temperature Τs ({approximately equal} 90 K) [5], it may arise from orbital ordering [6-9], spin fluctuations [10-12], or hidden magnetic quadrupolar order [13,14]. Here we use inelastic neutron scattering (INS) on detwinned single crystals of FeSe to demonstrate that are low energies, Ε = 6-11 meV, the intensity of spin excitations at the antiferromagnetic (AF) wave vector QAF = (±1,0) completely dominates that of (0, ±1) in the normal state. Remarkable, the two-fold (C2) anisotropy is reduced at lower energies 3-5 meV, indicating the existence of a gaped four-fold (C4) mode with incommensurate dispersion around 5-6 meV. Upon entering the superconducting state, however, the strong nematic anisotropy is again reflected in the spin resonance (Ε = 3.7 meV) which is only exhibited at QAF [17-20]. These results are consistent with angle resolved photoemission spectroscopy (ARPES) [21-23] and scanning tunneling microscopy (STM) [24-26] experiments, indicating that both nematicity and superconductivity are driven by spin fluctuations dominated by the dyz orbitals of Fe atoms that have weight on the hole and electron Fermi surfaces [Fig. 1(b)[2].
Nature Materials


superconductivity, iron selenide, spin fluctuation
Created July 1, 2019, Updated January 16, 2020