Nematic spin fluid in the tetragonal phase of BaFe2As2 - Condensed Matter > SuperconductivityReport as inadecuate

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Abstract: Magnetic interactions are generally believed to play a key role in mediatingelectron pairing for superconductivity in iron arsenides; yet their characteris only partially understood. Experimentally, the antiferromagnetic AFtransition is always preceded by or coincident with a tetragonal toorthorhombic structural distortion. Although it has been suggested that thislattice distortion is driven by an electronic nematic phase, where aspontaneously generated electronic liquid crystal state breaks the C4rotational symmetry of the paramagnetic state, experimental evidence forelectronic anisotropy has been either in the low-temperature orthorhombic phaseor the tetragonal phase under uniaxial pressure that breaks this symmetry. Herewe use inelastic neutron scattering to demonstrate the presence of a largein-plane spin anisotropy above TN in the unstressed tetragonal phase ofBaFe2As2. In the low-temperature orthorhombic phase, we find highly anisotropicspin waves with a large damping along the AF a-axis direction. On warming thesystem to the paramagnetic tetragonal phase, the low-energy spin waves evolveinto quasi-elastic excitations, while the anisotropic spin excitations near thezone boundary persist. These results strongly suggest that the spin nematicitywe find in the tetragonal phase of BaFe2As2 is the source of the electronic andorbital anisotropy observed above TN by other probes, and has profoundconsequences for the physics of these materials.

Author: Leland W. Harriger, Huiqian Luo, Mengshu Liu, T. G. Perring, C. Frost, Jiangping Hu, M. R. Norman, Pengcheng Dai


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