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Anisotropic spin fluctuations in detwinned FeSe
Tong Chen1, Youzhe Chen2, Andreas Kreisel3
1Department of Physics and Astronomy, Rice University, Houston, TX, USA.
Nature Materials
|May 22, 2019
Summary
Superconductivity in iron selenide (FeSe) arises from a nematic phase. This study reveals anisotropic spin excitations in the normal and superconducting states, suggesting a highly anisotropic superconducting gap driven by spin fluctuations.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Materials
Background:
- Superconductivity in iron selenide (FeSe) is linked to a preceding nematic phase.
- This nematic phase breaks the four-fold rotational symmetry of the iron plane.
- Potential origins include orbital ordering, spin fluctuations, or magnetic quadrupolar order.
Purpose of the Study:
- To investigate the nature of spin excitations in the nematic phase of FeSe.
- To understand the relationship between nematicity and superconductivity in FeSe.
- To determine the role of spin fluctuations in the anisotropic superconducting gap.
Main Methods:
- Inelastic neutron scattering was performed on detwinned single crystals of FeSe.
- Crystals were mounted on a BaFe2As2 substrate to achieve detwinning.
- Spin excitations were measured at various energy transfers and wave vectors.
Main Results:
- Spin excitations showed two-fold (C2) anisotropy at low energies (6-11 meV) in the normal state, concentrated at antiferromagnetic wave vectors QAF = (±1, 0).
- A gapped four-fold (C4) mode was indicated by reduced anisotropy at lower energies (3-5 meV).
- In the superconducting state, a spin resonance (3.6 meV) at QAF exhibited incommensurate scattering (5-6 meV), reflecting strong nematic anisotropy.
Conclusions:
- The results highlight the extreme electronic anisotropy inherent in the nematic phase of FeSe.
- The observed spin dynamics are consistent with a highly anisotropic superconducting gap.
- Spin fluctuations are strongly implicated as the driving mechanism for this anisotropy.
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