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Updated: May 18, 2026

Visualizing Uniaxial-strain Manipulation of Antiferromagnetic Domains in Fe1+YTe Using a Spin-polarized Scanning Tunneling Microscope
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Octet-line node structure of superconducting order parameter in KFe2As2.

K Okazaki1, Y Ota, Y Kotani

  • 1Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan. okazaki@issp.u-tokyo.ac.jp

Science (New York, N.Y.)
|September 18, 2012
PubMed
Summary
This summary is machine-generated.

KFe(2)As(2) exhibits superconductivity despite lacking electron Fermi surfaces. Its nodal s-wave nature reveals a unique multi-gap structure with FS-selective nodal features, suggesting universal A(1g) symmetry in iron-pnictides.

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Superconductivity

Background:

  • Iron-pnictide superconductors typically rely on interband interactions between hole and electron Fermi surfaces (FSs).
  • KFe(2)As(2) presents an anomaly, possessing multiple hole FSs but no electron FS, yet still displaying superconductivity.

Purpose of the Study:

  • To investigate the unconventional superconductivity in KFe(2)As(2).
  • To elucidate the Fermi surface (FS) structure and superconducting gap symmetry in KFe(2)As(2).

Main Methods:

  • Ultrahigh-resolution laser angle-resolved photoemission spectroscopy (ARPES).

Main Results:

  • KFe(2)As(2) is identified as a nodal s-wave superconductor.
  • A highly unusual, FS-selective multi-gap structure was observed: a nodeless gap on the inner FS, an "octet-line node" gap on the middle FS, and an almost-zero gap on the outer FS.
  • The observed gap structure suggests frustration between competing pairing interactions on hole FSs, leading to an eightfold sign reversal.

Conclusions:

  • The findings challenge conventional models of iron-pnictide superconductivity.
  • The universal A(1g) superconducting symmetry is proposed for iron-pnictides, irrespective of diverse gap functions.
  • This study provides critical insights into the complex pairing mechanisms in iron-based superconductors.