Cooper pairing in the iron-based high-Tc superconductors1, 2, 3 is often conjectured to involve bosonic fluctuations. Among the candidates are antiferromagnetic spin fluctuations1, 4, 5 and d-orbital fluctuations amplified by phonons6, 7. Any such electron–boson interaction should alter the electron’s ‘self-energy’, and then become detectable through consequent modifications in the energy dependence of the electron’s momentum and lifetime8, 9, 10. Here we introduce a novel theoretical/experimental approach aimed at uniquely identifying the relevant fluctuations of iron-based superconductors by measuring effects of their self-energy. We use innovative quasiparticle interference (QPI) imaging11 techniques in LiFeAs to reveal strongly momentum-space anisotropic self-energy signatures that are focused along the Fe–Fe (interband scattering) direction, where the spin fluctuations of LiFeAs are concentrated. These effects coincide in energy with perturbations to the density of states N(ω) usually associated with the Cooper pairing interaction. We show that all the measured phenomena comprise the predicted QPI ‘fingerprint’ of a self-energy due to antiferromagnetic spin fluctuations, thereby distinguishing them as the predominant electron–boson interaction.
At a glance
- The electron-pairing mechanism of iron-based superconductors. Science 332, 200–204 (2011). &
- Gap symmetry and structure of Fe-based superconductors. Rep. Prog. Phys. 74, 124508 (2011). , &
- A common thread: The pairing interaction for unconventional superconductors. Rev. Mod. Phys. 84, 1383–1417 (2012).
- Unconventional superconductivity with a sign reversal in the order parameter of LaFeAsO1−xFx. Phys. Rev. Lett. 101, 057003 (2008). , , &
- Unconventional pairing originating from the disconnected Fermi surfaces of superconducting LaFeAsO1−xFx. Phys. Rev. Lett. 101, 087004 (2008). et al.
- Orbital fluctuation mechanism for superconductivity in iron-based compounds. Phys. Rev. B 78, 195114 (2008). , &
- Orbital-fluctuation-mediated superconductivity in iron pnictides: Analysis of the five-orbital Hubbard–Holstein model. Phys. Rev. Lett. 104, 157001 (2010). &
- Spectral analysis for the iron-based superconductors: Anisotropic spin-fluctuations and fully gapped s±-wave superconductivity. Phys. Rev. B 82, 134527 (2010). , &
- Electronic dispersion anomalies in iron pnictide superconductors. Phys. Rev. Lett. 106, 047003 (2011). , &
- Effect of spin fluctuations on the electronic structure in iron-based superconductors. Phys. Rev. B 86, 064528 (2012). , &
- Anisotropic energy gaps of iron-based superconductivity from intraband quasiparticle interference in LiFeAs. Science 336, 563–567 (2012). et al.
- Incommensurate magnetic fluctuations and Fermi surface topology in LiFeAs. Phys. Rev. B 86, 174519 (2012). et al.
- Momentum dependence of superconducting gap, strong-coupling dispersion kink, and tightly bound Cooper pairs in the high-Tc (Sr, Ba)1−x(K, Na)xFe2As2 superconductors. Phys. Rev. B 78, 184508 (2008). et al.
- Temperature and doping-dependent renormalization effects of the low energy electronic structure of Ba1−xKxFe2As2 single crystals. Phys. Rev. Lett. 102, 167001 (2009). et al.
- Angle-resolved photoemission spectroscopy of the Fe-based Ba0.6K0.4Fe2As2 high-temperature superconductor: Evidence for an orbital selective electron-mode coupling. Phys. Rev. Lett. 102, 047003 (2009). et al.
- Angle-resolved photoemission spectroscopy of superconducting LiFeAs: Evidence for strong electron–phonon coupling. Phys. Rev. B 83, 134513 (2011). et al.
- One-sign order parameter in iron based superconductor. Symmetry 4, 251–264 (2012). et al.
- Scanning tunneling spectroscopy of superconducting LiFeAs single crystals: Evidence for two nodeless energy gaps and coupling to a bosonic mode. Phys. Rev. Lett. 109, 087002 (2012). et al.
- Quasi-particle interference probe of the self-energy. New J. Phys. 16, 023003 (2014). &
- Vol. 2 (eds Bennemann, K. H. & Ketterson, J. B.) Ch. 3, (Springer, 2008). & in Superconductivity
- Tight-binding models for the iron-based superconductors. Phys. Rev. B 80, 104503 (2009). &
- Antiferromagnetic spin fluctuations in LiFeAs observed by neutron scattering. Phys. Rev. B 83, 220514 (2011). et al.
- Inelastic neutron-scattering measurements of incommensurate magnetic excitations on superconducting LiFeAs single crystals. Phys. Rev. Lett. 108, 117001 (2012). et al.
- Three-dimensional electronic structure and interband nesting in the stoichiometric superconductor LiFeAs. Phys. Rev. B 85, 094509 (2012). et al.
- Unconventional anisotropic s-wave superconducting gaps of the LiFeAs iron-pnictide superconductor. Phys. Rev. Lett. 108, 037002 (2012). et al.
- Optical spectroscopy of superconducting Ba0.55K0.45Fe2As2: Evidence for strong coupling to low-energy bosons. Phys. Rev. Lett. 102, 187003 (2009). et al.
- Local quasiparticle density of states of superconducting SmFeAsO1−xFx single crystals: Evidence for spin-mediated pairing. Phys. Rev. Lett. 105, 167005 (2010). et al.
- Eliashberg analysis of optical spectra reveals a strong coupling of charge carriers to spin fluctuations in doped iron-pnictide BaFe2As2 superconductors. Phys. Rev. B 82, 144519 (2010). et al.
- Self-energy effects and electron–phonon coupling in Fe–As superconductors. J. Phys. Condens. Matter 22, 115802 (2010). et al.
- Inelastic neutron scattering study of the resonance mode in the optimally doped pnictide superconductor LaFeAsO0.92F0.08. Phys. Rev. B 82, 172508 (2010). et al.
- Evidence of a spin resonance mode in the iron-based superconductor Ba0.6K0.4Fe2As2 from scanning tunneling spectroscopy. Phys. Rev. Lett. 108, 227002 (2012). et al.
- Visualizing the microscopic coexistence of spin density wave and superconductivity in underdoped NaFe1−xCoxAs. Nature Commun. 4, 1596 (2013). et al.
- Antiferromagnetic spin excitations in single crystals of nonsuperconducting Li1−xFeAs. Phys. Rev. B 83, 220515 (2011). et al.