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Iron pnictides and chalcogenides: a new paradigm for superconductivity

Abstract

Superconductivity is a remarkably widespread phenomenon that is observed in most metals cooled to very low temperatures. The ubiquity of such conventional superconductors, and the wide range of associated critical temperatures, is readily understood in terms of the well-known Bardeen–Cooper–Schrieffer theory. Occasionally, however, unconventional superconductors are found, such as the iron-based materials, which extend and defy this understanding in unexpected ways. In the case of the iron-based superconductors, this includes the different ways in which the presence of multiple atomic orbitals can manifest in unconventional superconductivity, giving rise to a rich landscape of gap structures that share the same dominant pairing mechanism. In addition, these materials have also led to insights into the unusual metallic state governed by the Hund’s interaction, the control and mechanisms of electronic nematicity, the impact of magnetic fluctuations and quantum criticality, and the importance of topology in correlated states. Over the fourteen years since their discovery, iron-based superconductors have proven to be a testing ground for the development of novel experimental tools and theoretical approaches, both of which have extensively influenced the wider field of quantum materials.

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Fig. 1: General structural and electronic properties.
Fig. 2: Electronic correlations and orbital differentiation.
Fig. 3: Dual local–itinerant nature of magnetism.
Fig. 4: Electronic nematic order and its coupling to the lattice.
Fig. 5: Superconducting gap structures and gap symmetries.
Fig. 6: Band inversion and topological phenomena.

References

  1. Keimer, B., Kivelson, S. A., Norman, M. R., Uchida, S. & Zaanen, J. From quantum matter to high-temperature superconductivity in copper oxides. Nature 518, 179–186 (2015).

    CAS  ADS  PubMed  Google Scholar 

  2. Scalapino, D. J. A common thread: the pairing interaction for unconventional superconductors. Rev. Mod. Phys. 84, 1383–1417 (2012).

    CAS  ADS  Google Scholar 

  3. Kamihara, Y., Watanabe, T., Hirano, M. & Hosono, H. Iron-based layered superconductor LaO1−xFxFeAs (x = 0.05−0.12) with Tc = 26 K. J. Am. Chem. Soc. 130, 3296–3297 (2008). The seminal observation of superconductivity in an iron-arsenide compound.

    CAS  PubMed  Google Scholar 

  4. Mazin, I. I., Singh, D. J., Johannes, M. D. & Du, M. H. Unconventional superconductivity with a sign reversal in the order parameter of LaFeAsO1−xFx. Phys. Rev. Lett. 101, 057003 (2008). Theoretical proposal that the s+− superconducting state in FeSCs is mediated by spin fluctuations.

    CAS  ADS  PubMed  Google Scholar 

  5. Kuroki, K., Usui, H., Onari, S., Arita, R. & Aoki, H. Pnictogen height as a possible switch between high-Tc nodeless and low-Tc nodal pairings in the iron-based superconductors. Phys. Rev. B 79, 224511 (2009). RPA calculation that shows the impact of the pnictogen height on the superconducting state.

    ADS  Google Scholar 

  6. Hirschfeld, P. J., Korshunov, M. M. & Mazin, I. I. Gap symmetry and structure of Fe-based superconductors. Rep. Prog. Phys. 74, 124508 (2011).

    ADS  Google Scholar 

  7. Chubukov, A. V. Pairing mechanism in Fe-based superconductors. Annu. Rev. Condens. Matter Phys. 3, 57–92 (2012). A pedagogical review that compares the RPA and renormalization group approaches to describe superconductivity in FeSCs.

    CAS  Google Scholar 

  8. Wang, F. & Lee, D.-H. The electron-pairing mechanism of iron-based superconductors. Science 332, 200–204 (2011).

    CAS  ADS  PubMed  Google Scholar 

  9. Haule, K. & Kotliar, G. Coherence–incoherence crossover in the normal state of iron oxypnictides and importance of Hund’s rule coupling. New J. Phys. 11, 025021 (2009). This theoretical work predicted the coherence–incoherence crossover caused by the Hund’s coupling, which later led to the concept of a Hund metal.

    ADS  Google Scholar 

  10. Yin, Z., Haule, K. & Kotliar, G. Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides. Nat. Mater. 10, 932–935 (2011). This study provides principles for organizing the families of FeSCs by their correlation strength and differentiation of the dxy orbitals.

    CAS  ADS  PubMed  Google Scholar 

  11. Stadler, K. M., Yin, Z. P., von Delft, J., Kotliar, G. & Weichselbaum, A. Dynamical mean-field theory plus numerical renormalization-group study of spin-orbital separation in a three-band Hund metal. Phys. Rev. Lett. 115, 136401 (2015).

    CAS  ADS  PubMed  Google Scholar 

  12. de’ Medici, L., Hassan, S. R., Capone, M. & Dai, X. Orbital-selective Mott transition out of band degeneracy lifting. Phys. Rev. Lett. 102, 126401 (2009).

    ADS  PubMed  Google Scholar 

  13. Bascones, E., Valenzuela, B. & Calderón, M. J. Orbital differentiation and the role of orbital ordering in the magnetic state of Fe superconductors. Phys. Rev. B 86, 174508 (2012).

    ADS  Google Scholar 

  14. Yu, R. & Si, Q. Orbital-selective Mott phase in multiorbital models for alkaline iron selenides K1−xFe2−ySe2. Phys. Rev. Lett. 110, 146402 (2013).

    ADS  PubMed  Google Scholar 

  15. de’ Medici, L., Giovannetti, G. & Capone, M. Selective Mott physics as a key to iron superconductors. Phys. Rev. Lett. 112, 177001 (2014).

    ADS  PubMed  Google Scholar 

  16. Georges, A., Medici, L. D. & Mravlje, J. Strong correlations from Hund’s coupling. Annu. Rev. Condens. Matter Phys. 4, 137–178 (2013).

    CAS  ADS  Google Scholar 

  17. Dai, P. Antiferromagnetic order and spin dynamics in iron-based superconductors. Rev. Mod. Phys. 87, 855–896 (2015).

    MathSciNet  CAS  ADS  Google Scholar 

  18. Lumsden, M. D. & Christianson, A. D. Magnetism in Fe-based superconductors. J. Phys. Condens. Matter 22, 203203 (2010). A topical review that surveys early neutron scattering data on FeSCs, including the observation of spin-resonance modes in the superconducting state.

    CAS  ADS  PubMed  Google Scholar 

  19. Inosov, D. et al. Normal-state spin dynamics and temperature-dependent spin-resonance energy in optimally doped BaFe1.85Co0.15As2. Nat. Phys. 6, 178–181 (2010).

    CAS  Google Scholar 

  20. Fernandes, R. M., Chubukov, A. V. & Schmalian, J. What drives nematic order in iron-based superconductors? Nat. Phys. 10, 97–104 (2014).

    CAS  Google Scholar 

  21. Fradkin, E., Kivelson, S. A., Lawler, M. J., Eisenstein, J. P. & Mackenzie, A. P. Nematic Fermi fluids in condensed matter physics. Annu. Rev. Condens. Matter Phys. 1, 153–178 (2010).

    CAS  ADS  Google Scholar 

  22. Chu, J.-H., Kuo, H.-H., Analytis, J. G. & Fisher, I. R. Divergent nematic susceptibility in an iron arsenide superconductor. Science 337, 710–712 (2012). Elastoresistivity measurements reveal the presence of nematic fluctuations across the phase diagram of an FeSC compound.

    CAS  ADS  PubMed  Google Scholar 

  23. Böhmer, A. E. et al. Nematic susceptibility of hole-doped and electron-doped BaFe2As2 iron-based superconductors from shear modulus measurements. Phys. Rev. Lett. 112, 047001 (2014).

    ADS  PubMed  Google Scholar 

  24. Gallais, Y. et al. Observation of incipient charge nematicity in Ba(Fe1−XCoX)2As2. Phys. Rev. Lett. 111, 267001 (2013).

    CAS  ADS  PubMed  Google Scholar 

  25. Zhang, P. et al. Observation of topological superconductivity on the surface of an iron-based superconductor. Science 360, 182–186 (2018). ARPES measurements reveal surface topological spin-helical states in FeTe1−xSex.

    ADS  PubMed  Google Scholar 

  26. Singh, D. J. & Du, M.-H. Density functional study of LaFeAsO1−xFx: a low carrier density superconductor near itinerant magnetism. Phys. Rev. Lett. 100, 237003 (2008).

    CAS  ADS  PubMed  Google Scholar 

  27. Eschrig, H. & Koepernik, K. Tight-binding models for the iron-based superconductors. Phys. Rev. B 80, 104503 (2009).

    ADS  Google Scholar 

  28. Cvetkovic, V. & Vafek, O. Space group symmetry, spin–orbit coupling, and the low-energy effective Hamiltonian for iron-based superconductors. Phys. Rev. B 88, 134510 (2013).

    ADS  Google Scholar 

  29. Borisenko, S. et al. Direct observation of spin–orbit coupling in iron-based superconductors. Nat. Phys. 12, 311–317 (2016).

    CAS  Google Scholar 

  30. Wang, Z. et al. Topological nature of the FeSe0.5Te0.5 superconductor. Phys. Rev. B 92, 115119 (2015).

    ADS  Google Scholar 

  31. Yang, W. L. et al. Evidence for weak electronic correlations in iron pnictides. Phys. Rev. B 80, 014508 (2009).

    ADS  Google Scholar 

  32. Coldea, A. I. Electronic nematic states tuned by isoelectronic substitution in bulk FeSe1−xSx. Front. Phys. 8, 594500 (2021).

    Google Scholar 

  33. Richard, P., Qian, T. & Ding, H. ARPES measurements of the superconducting gap of Fe-based superconductors and their implications to the pairing mechanism. J. Phys. Condens. Matter 27, 293203 (2015).

    CAS  PubMed  Google Scholar 

  34. Yi, M., Zhang, Y., Shen, Z.-X. & Lu, D. Role of the orbital degree of freedom in iron-based superconductors. npj Quantum Mater. 2, 57 (2017).

    ADS  Google Scholar 

  35. Carrington, A. Quantum oscillation studies of the Fermi surface of iron-pnictide superconductors. Rep. Prog. Phys. 74, 124507 (2011).

    ADS  Google Scholar 

  36. Coldea, A. I. et al. Fermi surface of superconducting LaFePO determined from quantum oscillations. Phys. Rev. Lett. 101, 216402 (2008).

    CAS  ADS  PubMed  Google Scholar 

  37. Qazilbash, M. et al. Electronic correlations in the iron pnictides. Nat. Phys. 5, 647–650 (2009).

    CAS  Google Scholar 

  38. Haule, K., Shim, J. H. & Kotliar, G. Correlated electronic structure of LaO1−xFxFeAs. Phys. Rev. Lett. 100, 226402 (2008).

    CAS  ADS  PubMed  Google Scholar 

  39. Skornyakov, S. L. et al. Classification of the electronic correlation strength in the iron pnictides: the case of the parent compound BaFe2As2. Phys. Rev. B 80, 092501 (2009).

    ADS  Google Scholar 

  40. Werner, P. et al. Satellites and large doping and temperature dependence of electronic properties in hole-doped BaFe2As2. Nat. Phys. 8, 331–337 (2012).

    CAS  Google Scholar 

  41. Ferber, J., Foyevtsova, K., Valentí, R. & Jeschke, H. O. LDA + DMFT study of the effects of correlation in LiFeAs. Phys. Rev. B 85, 094505 (2012).

    ADS  Google Scholar 

  42. Lee, G. et al. Orbital selective Fermi surface shifts and mechanism of high Tc superconductivity in correlated AFeAs (A = Li, Na). Phys. Rev. Lett. 109, 177001 (2012).

    ADS  PubMed  Google Scholar 

  43. Borisenko, S. V. et al. Superconductivity without nesting in LiFeAs. Phys. Rev. Lett. 105, 067002 (2010).

    CAS  ADS  PubMed  Google Scholar 

  44. Fanfarillo, L. et al. Orbital-dependent Fermi surface shrinking as a fingerprint of nematicity in FeSe. Phys. Rev. B 94, 155138 (2016).

    ADS  Google Scholar 

  45. Ortenzi, L., Cappelluti, E., Benfatto, L. & Pietronero, L. Fermi-surface shrinking and interband coupling in iron-based pnictides. Phys. Rev. Lett. 103, 046404 (2009).

    CAS  ADS  PubMed  Google Scholar 

  46. Zantout, K., Backes, S. & Valentí, R. Effect of nonlocal correlations on the electronic structure of LiFeAs. Phys. Rev. Lett. 123, 256401 (2019).

    CAS  ADS  PubMed  Google Scholar 

  47. Tomczak, J. M., van Schilfgaarde, M. & Kotliar, G. Many-body effects in iron pnictides and chalcogenides: nonlocal versus dynamic origin of effective masses. Phys. Rev. Lett. 109, 237010 (2012).

    ADS  PubMed  Google Scholar 

  48. van der Marel, D. & Sawatzky, G. A. Electron–electron interaction and localization in d and f transition metals. Phys. Rev. B 37, 10674 (1988).

    Google Scholar 

  49. Hardy, F. et al. Evidence of strong correlations and coherence–incoherence crossover in the iron pnictide superconductor KFe2As2. Phys. Rev. Lett. 111, 027002 (2013).

    CAS  ADS  PubMed  Google Scholar 

  50. Yin, Z. P., Haule, K. & Kotliar, G. Fractional power-law behavior and its origin in iron-chalcogenide and ruthenate superconductors: insights from first-principles calculations. Phys. Rev. B 86, 195141 (2012).

    ADS  Google Scholar 

  51. Kreisel, A., Hirschfeld, P. J. & Andersen, B. M. On the remarkable superconductivity of FeSe and its close cousins. Symmetry 12, 1402 (2020).

    CAS  Google Scholar 

  52. Yu, R., Zhu, J.-X. & Si, Q. Orbital-selective superconductivity, gap anisotropy, and spin resonance excitations in a multiorbital tJ1J2 model for iron pnictides. Phys. Rev. B 89, 024509 (2014).

    ADS  Google Scholar 

  53. Fanfarillo, L., Valli, A. & Capone, M. Synergy between Hund-driven correlations and boson-mediated superconductivity. Phys. Rev. Lett. 125, 177001 (2020).

    CAS  ADS  PubMed  Google Scholar 

  54. Sprau, P. O. et al. Discovery of orbital-selective Cooper pairing in FeSe. Science 357, 75–80 (2017). STM observation of a strong gap anisotropy in FeSe and proposal of orbital differentiation inside the superconducting state.

    CAS  ADS  PubMed  Google Scholar 

  55. Rhodes, L. C. et al. Scaling of the superconducting gap with orbital character in FeSe. Phys. Rev. B 98, 180503 (2018).

    CAS  ADS  Google Scholar 

  56. Liu, D. et al. Orbital origin of extremely anisotropic superconducting gap in nematic phase of FeSe superconductor. Phys. Rev. X 8, 031033 (2018).

    CAS  Google Scholar 

  57. Yin, Z., Haule, K. & Kotliar, G. Spin dynamics and orbital-antiphase pairing symmetry in iron-based superconductors. Nat. Phys. 10, 845–850 (2014).

    CAS  Google Scholar 

  58. Pelliciari, J. et al. Magnetic moment evolution and spin freezing in doped BaFe2As2. Sci. Rep. 7, 8003 (2017).

    PubMed  PubMed Central  ADS  Google Scholar 

  59. Wang, M. et al. Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides. Nat. Commun. 4, 2874 (2013).

    ADS  PubMed  Google Scholar 

  60. Christensen, M. H., Kang, J., Andersen, B. M., Eremin, I. & Fernandes, R. M. Spin reorientation driven by the interplay between spin-orbit coupling and Hund’s rule coupling in iron pnictides. Phys. Rev. B 92, 214509 (2015).

    ADS  Google Scholar 

  61. Qureshi, N. et al. Inelastic neutron-scattering measurements of incommensurate magnetic excitations on superconducting LiFeAs single crystals. Phys. Rev. Lett. 108, 117001 (2012).

    CAS  ADS  PubMed  Google Scholar 

  62. Wang, Q. et al. Magnetic ground state of FeSe. Nat. Commun. 7, 12182 (2016).

    CAS  PubMed  PubMed Central  ADS  Google Scholar 

  63. Lumsden, M. D. et al. Evolution of spin excitations into the superconducting state in FeTe1−xSex. Nat. Phys. 6, 182–186 (2010).

    CAS  Google Scholar 

  64. Liu, T. et al. From (π, 0) magnetic order to superconductivity with (π, π) magnetic resonance in Fe1.02Te1−xSex. Nat. Mater. 9, 718–720 (2010).

    ADS  Google Scholar 

  65. Gastiasoro, M. N. & Andersen, B. M. Enhancement of magnetic stripe order in iron-pnictide superconductors from the interaction between conduction electrons and magnetic impurities. Phys. Rev. Lett. 113, 067002 (2014).

    CAS  ADS  PubMed  Google Scholar 

  66. Pratt, D. K. et al. Incommensurate spin-density wave order in electron-doped BaFe2As2 superconductors. Phys. Rev. Lett. 106, 257001 (2011).

    CAS  ADS  PubMed  Google Scholar 

  67. Allred, J. M. et al. Double-Q spin-density wave in iron arsenide superconductors. Nat. Phys. 12, 493–498 (2016).

    CAS  Google Scholar 

  68. Lorenzana, J., Seibold, G., Ortix, C. & Grilli, M. Competing orders in FeAs layers. Phys. Rev. Lett. 101, 186402 (2008).

    CAS  ADS  PubMed  Google Scholar 

  69. Fernandes, R. M., Kivelson, S. A. & Berg, E. Vestigial chiral and charge orders from bidirectional spin-density waves: application to the iron-based superconductors. Phys. Rev. B 93, 014511 (2016).

    ADS  Google Scholar 

  70. Meier, W. R. et al. Hedgehog spin-vortex crystal stabilized in a hole-doped iron-based superconductor. npj Quantum Mater. 3, 5 (2018).

    ADS  Google Scholar 

  71. Si, Q. & Abrahams, E. Strong correlations and magnetic frustration in the high Tc iron pnictides. Phys. Rev. Lett. 101, 076401 (2008).

    ADS  PubMed  Google Scholar 

  72. Seo, K., Bernevig, B. A. & Hu, J. Pairing symmetry in a two-orbital exchange coupling model of oxypnictides. Phys. Rev. Lett. 101, 206404 (2008).

    ADS  PubMed  Google Scholar 

  73. Dai, P., Hu, J. & Dagotto, E. Magnetism and its microscopic origin in iron-based high-temperature superconductors. Nat. Phys. 8, 709–718 (2012).

    CAS  Google Scholar 

  74. Eremin, I. & Chubukov, A. V. Magnetic degeneracy and hidden metallicity of the spin-density-wave state in ferropnictides. Phys. Rev. B 81, 024511 (2010).

    ADS  Google Scholar 

  75. Fernandes, R. M. & Chubukov, A. V. Low-energy microscopic models for iron-based superconductors: a review. Rep. Prog. Phys. 80, 014503 (2016).

    ADS  PubMed  Google Scholar 

  76. Yildirim, T. Origin of the 150-K anomaly in LaFeAsO: competing antiferromagnetic interactions, frustration, and a structural phase transition. Phys. Rev. Lett. 101, 057010 (2008).

    CAS  ADS  PubMed  Google Scholar 

  77. Glasbrenner, J. et al. Effect of magnetic frustration on nematicity and superconductivity in iron chalcogenides. Nat. Phys. 11, 953–958 (2015).

    CAS  Google Scholar 

  78. Hirayama, M., Misawa, T., Miyake, T. & Imada, M. Ab initio studies of magnetism in the iron chalcogenides FeTe and FeSe. J. Phys. Soc. Jpn 84, 093703 (2015).

    ADS  Google Scholar 

  79. Abrahams, E. & Si, Q. Quantum criticality in the iron pnictides and chalcogenides. J. Phys. Condens. Matter 23, 223201 (2011).

    ADS  PubMed  Google Scholar 

  80. Shibauchi, T., Carrington, A. & Matsuda, Y. A quantum critical point lying beneath the superconducting dome in iron pnictides. Annu. Rev. Condens. Matter Phys. 5, 113–135 (2014). A review of the evidence of quantum critical behaviour in FeSCs, including the observation of a sharp peak in the doping-dependent penetration depth.

    CAS  ADS  Google Scholar 

  81. Hayes, I. M. et al. Scaling between magnetic field and temperature in the high-temperature superconductor BaFe2 (As1−xPx)2. Nat. Phys. 12, 916–919 (2016).

    Google Scholar 

  82. Chowdhury, D., Swingle, B., Berg, E. & Sachdev, S. Singularity of the London penetration depth at quantum critical points in superconductors. Phys. Rev. Lett. 111, 157004 (2013).

    ADS  PubMed  Google Scholar 

  83. Levchenko, A., Vavilov, M. G., Khodas, M. & Chubukov, A. V. Enhancement of the London penetration depth in pnictides at the onset of spin-density-wave order under superconducting dome. Phys. Rev. Lett. 110, 177003 (2013).

    CAS  ADS  PubMed  Google Scholar 

  84. Lu, X. et al. Nematic spin correlations in the tetragonal state of uniaxial-strained BaFe2−xNixAs2. Science 345, 657–600 (2014). Inelastic neutron scattering experiments in a detwinned FeSC compound reveal the intertwining between nematic order and spin fluctuations.

    CAS  ADS  PubMed  Google Scholar 

  85. Chu, J.-H. et al. In-plane resistivity anisotropy in an underdoped iron arsenide superconductor. Science 329, 824–826 (2010).

    CAS  ADS  PubMed  Google Scholar 

  86. Mirri, C. et al. Origin of the resistive anisotropy in the electronic nematic phase of BaFe2As2 revealed by optical spectroscopy. Phys. Rev. Lett. 115, 107001 (2015).

    CAS  ADS  PubMed  Google Scholar 

  87. Chuang, T.-M. et al. Nematic electronic structure in the “parent” state of the iron-based superconductor Ca(Fe1−xCox)2As2. Science 327, 181–184 (2010).

    CAS  ADS  PubMed  Google Scholar 

  88. Liang, S., Moreo, A. & Dagotto, E. Nematic state of pnictides stabilized by interplay between spin, orbital, and lattice degrees of freedom. Phys. Rev. Lett. 111, 047004 (2013).

    ADS  PubMed  Google Scholar 

  89. Lee, C.-C., Yin, W.-G. & Ku, W. Ferro-orbital order and strong magnetic anisotropy in the parent compounds of iron-pnictide superconductors. Phys. Rev. Lett. 103, 267001 (2009).

    ADS  PubMed  Google Scholar 

  90. Lv, W., Krüger, F. & Phillips, P. Orbital ordering and unfrustrated (π, 0) magnetism from degenerate double exchange in the iron pnictides. Phys. Rev. B 82, 045125 (2010).

    ADS  Google Scholar 

  91. Fang, C., Yao, H., W.-F. Tsai, J. Hu, & S. A. Kivelson, Theory of electron nematic order in LaFeAsO. Phys. Rev. B 77, 224509 (2008).

    ADS  Google Scholar 

  92. Xu, C., Müller, M. & Sachdev, S. Ising and spin orders in the iron-based superconductors. Phys. Rev. B 78, 020501 (2008).

    ADS  Google Scholar 

  93. Fernandes, R. M., Orth, P. P. & Schmalian, J. Intertwined vestigial order in quantum materials: nematicity and beyond. Annu. Rev. Condens. Matter Phys. 10, 133–154 (2019).

    ADS  Google Scholar 

  94. Wang, F., Kivelson, S. A. & LeeD.-H. Nematicity and quantum paramagnetism in FeSe. Nat. Phys. 11, 959–963 (2015).

    CAS  Google Scholar 

  95. Fernandes, R. M., Chubukov, A. V., Knolle, J., Eremin, I. & Schmalian, J. Preemptive nematic order, pseudogap, and orbital order in the iron pnictides. Phys. Rev. B 85, 024534 (2012).

    ADS  Google Scholar 

  96. Gati, E., Xiang, L., Bud’ko, S. L. & Canfield, P. C. Role of the Fermi surface for the pressure-tuned nematic transition in the BaFe2As2 family. Phys. Rev. B 100, 064512 (2019).

    CAS  ADS  Google Scholar 

  97. Fernandes, R. M., Böhmer, A. E., Meingast, C. & Schmalian, J. Scaling between magnetic and lattice fluctuations in iron pnictide superconductors. Phys. Rev. Lett. 111, 137001 (2013).

    ADS  PubMed  Google Scholar 

  98. Baek, S. et al. Orbital-driven nematicity in FeSe. Nat. Mater. 14, 210–214 (2015).

    CAS  ADS  PubMed  Google Scholar 

  99. Böhmer, A. E. et al. Distinct pressure evolution of coupled nematic and magnetic orders in FeSe. Phys. Rev. B 100, 064515 (2019).

    ADS  Google Scholar 

  100. Suzuki, Y. et al. Momentum-dependent sign inversion of orbital order in superconducting FeSe. Phys. Rev. B 92, 205117 (2015).

    ADS  Google Scholar 

  101. Lederer, S., Schattner, Y., Berg, E. & Kivelson, S. A. Superconductivity and non-Fermi liquid behavior near a nematic quantum critical point. Proc. Natl Acad. Sci. USA 114, 4905–4910 (2017).

    CAS  PubMed  PubMed Central  ADS  Google Scholar 

  102. Klein, A. & Chubukov, A. V. Superconductivity near a nematic quantum critical point: interplay between hot and lukewarm regions. Phys. Rev. B 98, 220501 (2018).

    CAS  ADS  Google Scholar 

  103. Worasaran, T. et al. Nematic quantum criticality in an Fe-based superconductor revealed by strain-tuning. Science 372, 973–977 (2021).

    CAS  PubMed  Google Scholar 

  104. Shibauchi, T., Hanaguri, T. & Matsuda, Y. Exotic superconducting states in FeSe-based materials. J. Phys. Soc. Jpn 89, 102002 (2020).

    ADS  Google Scholar 

  105. Reiss, P. et al. Quenched nematic criticality and two superconducting domes in an iron-based superconductor. Nat. Phys. 16, 89–94 (2020).

    CAS  Google Scholar 

  106. Huang, D. & Hoffman, J. E. Monolayer FeSe on SrTiO3. Annu. Rev. Condens. Matter Phys. 8, 311–336 (2017).

    CAS  ADS  Google Scholar 

  107. Hosono, H., Yamamoto, A., Hiramatsu, H. & Ma, Y. Recent advances in iron-based superconductors toward applications. Mater. Today 21, 278–302 (2018).

    CAS  Google Scholar 

  108. Boeri, L., Dolgov, O. V. & Golubov, A. A. Is LaFeAsO1−xFx an electron–phonon superconductor? Phys. Rev. Lett. 101, 026403 (2008).

    CAS  ADS  PubMed  Google Scholar 

  109. Mandal, S., Cohen, R. E. & Haule, K. Strong pressure-dependent electron–phonon coupling in FeSe. Phys. Rev. B 89, 220502 (2014).

    ADS  Google Scholar 

  110. Lee, J. et al. Interfacial mode coupling as the origin of the enhancement of Tc in FeSe films on SrTiO3. Nature 515, 245–248 (2014). The observation of a connection between a substrate phonon mode and the enhancement of superconductivity in monolayer FeSe grown on SrTiO3.

    CAS  ADS  PubMed  Google Scholar 

  111. Thomale, R., Platt, C., Hanke, W., Hu, J. & Bernevig, B. A. Exotic d-wave superconducting state of strongly hole-doped KxBa1−xFe2As2. Phys. Rev. Lett. 107, 117001 (2011).

    ADS  PubMed  Google Scholar 

  112. Paul, I. & Garst, M. Lattice effects on nematic quantum criticality in metals. Phys. Rev. Lett. 118, 227601 (2017).

    CAS  ADS  PubMed  Google Scholar 

  113. Kontani, H. & Onari, S. Orbital-fluctuation-mediated superconductivity in iron pnictides: analysis of the five-orbital Hubbard–Holstein model. Phys. Rev. Lett. 104, 157001 (2010).

    ADS  PubMed  Google Scholar 

  114. Chen, C.-T., Tsuei, C., Ketchen, M., Ren, Z.-A. & Zhao, Z. Integer and half-integer flux-quantum transitions in a niobium-iron pnictide loop. Nat. Phys. 6, 260–264 (2010).

    CAS  Google Scholar 

  115. Hanaguri, T., Niitaka, S., Kuroki, K. & Takagi, H. Unconventional s-wave superconductivity in Fe(Se,Te). Science 328, 474–476 (2010).

    CAS  ADS  PubMed  Google Scholar 

  116. Cho, K., Kończykowski, M., Teknowijoyo, S., Tanatar, M. A. & Prozorov, R. Using electron irradiation to probe iron-based superconductors. Supercond. Sci. Technol. 31, 064002 (2018).

    ADS  Google Scholar 

  117. Yang, H. et al. In-gap quasiparticle excitations induced by non-magnetic Cu impurities in Na(Fe0.96Co0.03Cu0.01)As revealed by scanning tunnelling spectroscopy. Nat. Commun. 4, 2749 (2013).

    ADS  PubMed  Google Scholar 

  118. Okazaki, K. et al. Octet-line node structure of superconducting order parameter in KFe2As2. Science 337, 1314–1317 (2012). Direct observation of accidental nodes in a hole-doped FeSC compound via laser ARPES measurements.

    CAS  ADS  PubMed  Google Scholar 

  119. Lee, T.-H., Chubukov, A. V., Miao, H. & Kotliar, G. Pairing mechanism in Hund’s metal superconductors and the universality of the superconducting gap to critical temperature ratio. Phys. Rev. Lett. 121, 187003 (2018).

    CAS  ADS  PubMed  Google Scholar 

  120. Stanev, V. & Tešanović, Z. Three-band superconductivity and the order parameter that breaks time-reversal symmetry. Phys. Rev. B 81, 134522 (2010).

    ADS  Google Scholar 

  121. Lee, W.-C., Zhang, S.-C. & Wu, C. Pairing state with a time-reversal symmetry breaking in FeAs-based superconductors. Phys. Rev. Lett. 102, 217002 (2009).

    ADS  PubMed  Google Scholar 

  122. Grinenko, V. et al. Superconductivity with broken time-reversal symmetry inside a superconducting s-wave state. Nat. Phys. 16, 789–794 (2020).

    CAS  Google Scholar 

  123. Kretzschmar, F. et al. Raman-scattering detection of nearly degenerate s-wave and d-wave pairing channels in iron-based Ba0.6K0.4Fe2As2 and Rb0.8Fe1.6Se2 superconductors. Phys. Rev. Lett. 110, 187002 (2013).

    CAS  ADS  PubMed  Google Scholar 

  124. Thorsmølle, V. K. et al. Critical quadrupole fluctuations and collective modes in iron pnictide superconductors. Phys. Rev. B 93, 054515 (2016).

    ADS  Google Scholar 

  125. Gallais, Y., Paul, I., Chauvière, L. & Schmalian, J. Nematic resonance in the Raman response of iron-based superconductors. Phys. Rev. Lett. 116, 017001 (2016).

    ADS  PubMed  Google Scholar 

  126. Tafti, F. et al. Sudden reversal in the pressure dependence of Tc in the iron-based superconductor KFe2As2. Nat. Phys. 9, 349–352 (2013).

    CAS  Google Scholar 

  127. Rinott, S. et al. Tuning across the BCS–BEC crossover in the multiband superconductor Fe1+ySexTe1−x: an angle-resolved photoemission study. Sci. Adv. 3, e1602372 (2017).

    PubMed  PubMed Central  ADS  Google Scholar 

  128. Lohani, H. et al. Band inversion and topology of the bulk electronic structure in FeSe0.45Te0.55. Phys. Rev. B 101, 245146 (2020).

    CAS  ADS  Google Scholar 

  129. Zhang, P. et al. Multiple topological states in iron-based superconductors. Nat. Phys. 15, 41–47 (2019).

    CAS  Google Scholar 

  130. König, E. J. & Coleman, P. Crystalline-symmetry-protected helical Majorana modes in the iron pnictides. Phys. Rev. Lett. 122, 207001 (2019).

    ADS  PubMed  Google Scholar 

  131. Kong, L. et al. Half-integer level shift of vortex bound states in an iron-based superconductor. Nat. Phys. 15, 1181–1187 (2019).

    CAS  Google Scholar 

  132. Wang, D. et al. Evidence for Majorana bound states in an iron-based superconductor. Science 362, 333–335 (2018). STM measurements reveal a zero-bias peak inside vortices of superconducting FeTe1−xSex suggestive of Majorana zero modes.

    CAS  ADS  PubMed  Google Scholar 

  133. Machida, T. et al. Zero-energy vortex bound state in the superconducting topological surface state of Fe(Se,Te). Nat. Mater. 18, 811–815 (2019).

    CAS  ADS  PubMed  Google Scholar 

  134. Yin, J.-X. et al. Observation of a robust zero-energy bound state in iron-based superconductor Fe(Te,Se). Nat. Phys. 11, 543–546 (2015).

    CAS  Google Scholar 

  135. Chen, C. et al. Atomic line defects and zero-energy end states in monolayer Fe(Te,Se) high-temperature superconductors. Nat. Phys. 16, 536–540 (2020).

    CAS  Google Scholar 

  136. Wang, Z. et al. Evidence for dispersing 1D Majorana channels in an iron-based superconductor. Science 367, 104–108 (2020).

    CAS  ADS  PubMed  Google Scholar 

  137. Zhang, R.-X., Cole, W. S. & Das Sarma, S. Helical hinge Majorana modes in iron-based superconductors. Phys. Rev. Lett. 122, 187001 (2019).

    CAS  ADS  PubMed  Google Scholar 

  138. Misawa, T., Nakamura, K. & Imada, M. Ab initio evidence for strong correlation associated with Mott proximity in iron-based superconductors. Phys. Rev. Lett. 108, 177007 (2012).

    ADS  PubMed  Google Scholar 

  139. Aichhorn, M., Biermann, S., Miyake, T., Georges, A. & Imada, M. Theoretical evidence for strong correlations and incoherent metallic state in FeSe. Phys. Rev. B 82, 064504 (2010).

    ADS  Google Scholar 

  140. Miyake, T., Nakamura, K., Arita, R. & Imada, M. Comparison of ab initio low-energy models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe, and FeTe: electron correlation and covalency. J. Phys. Soc. Jpn 79, 044705 (2010).

    ADS  Google Scholar 

  141. Zaki, N., Gu, G., Tsvelik, A., Wu, C. & Johnson, P. D. Time-reversal symmetry breaking in the Fe-chalcogenide superconductors. Proc. Natl Acad. Sci. USA 118, e2007241118 (2021).

    CAS  PubMed  PubMed Central  Google Scholar 

  142. Kong, L. et al. Majorana zero modes in impurity-assisted vortex of LiFeAs superconductor. Nat. Commun. 12, 4146 (2021).

    CAS  PubMed  PubMed Central  ADS  Google Scholar 

  143. Karahasanovic, U. & Schmalian, J. Elastic coupling and spin-driven nematicity in iron-based superconductors. Phys. Rev. B 93, 064520 (2016).

    ADS  Google Scholar 

  144. Dioguardi, A. P. et al. NMR evidence for inhomogeneous glassy behavior driven by nematic fluctuations in iron arsenide superconductors. Phys. Rev. B 92, 165116 (2015).

    ADS  Google Scholar 

  145. Frandsen, B. A., Wang, Q., Wu, S., Zhao, J. & Birgeneau, R. J. Quantitative characterization of short-range orthorhombic fluctuations in FeSe through pair distribution function analysis. Phys. Rev. B 100, 020504 (2019).

    CAS  ADS  Google Scholar 

  146. Kuo, H.-H., Chu, J.-H., Palmstrom, J. C., Kivelson, S. A. & Fisher, I. R. Ubiquitous signatures of nematic quantum criticality in optimally doped Fe-based superconductors. Science 352, 958–962 (2016).

    MathSciNet  CAS  MATH  ADS  PubMed  Google Scholar 

  147. Vafek, O. & Chubukov, A. V. Hund interaction, spin–orbit coupling, and the mechanism of superconductivity in strongly hole-doped iron pnictides. Phys. Rev. Lett. 118, 087003 (2017).

    ADS  PubMed  Google Scholar 

  148. Katayama, N. et al. Superconductivity in Ca1−xLaxFeAs2: a novel 112-type iron pnictide with arsenic zigzag bonds. J. Phys. Soc. Jpn 82, 123702 (2013).

    ADS  Google Scholar 

  149. Dagotto, E. Colloquium: The unexpected properties of alkali metal iron selenide superconductors. Rev. Mod. Phys. 85, 849–867 (2013).

    CAS  ADS  Google Scholar 

  150. Wu, S., Frandsen, B. A., Wang, M., Yi, M. & Birgeneau, R. Iron-based chalcogenide spin ladder BaFe2X3 (X = Se, S). J. Supercond. Nov. Magn. 33, 143–158 (2020).

    CAS  Google Scholar 

  151. Momma, K. & Izumi, F. VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl.Crystallogr. 44, 1272–1276 (2011).

    CAS  Google Scholar 

  152. Kong, L. & Ding, H. Emergent vortex Majorana zero mode in iron-based superconductors. Acta Phys. Sin. 69, 110301 (2020).

    ADS  Google Scholar 

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Acknowledgements

We thank all our co-authors and collaborators with whom we have had many discussions since the discovery of the iron-based superconductors. In particular, we thank H. Miao and T. H. Lee (Figs. 2 and 5), M. Christensen (Fig. 4) and L.-Y. Kong (Fig. 6) for their assistance in making some of the figures panels. R.M.F. was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division, under award number DE-SC0020045. A.I.C. acknowledges an EPSRC Career Acceleration Fellowship (EP/I004475/1) and the Oxford Centre for Applied Superconductivity (CFAS) for financial support. A.I.C. is grateful to the KITP programme ‘correlated20’, which was supported in part by the National Science Foundation under grant number NSF PHY-1748958. H.D. is supported by the National Natural Science Foundation of China (grant numbers 11888101 and 11674371), the Strategic Priority Research Program of the Chinese Academy of Sciences, China (grant numbers XDB28000000 and XDB07000000) and the Beijing Municipal Science and Technology Commission, China (grant number Z191100007219012). I.R.F. was supported by the US Department of Energy, Office of Basic Energy Sciences, under contract DE-AC02-76SF00515. P.J.H. was supported by the US Department of Energy, Office of Basic Sciences under grant number DE-FG02-05ER46236. G.K. was supported by NSF DMR-1733071.

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Fernandes, R.M., Coldea, A.I., Ding, H. et al. Iron pnictides and chalcogenides: a new paradigm for superconductivity. Nature 601, 35–44 (2022). https://doi.org/10.1038/s41586-021-04073-2

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