Electronic-Structure-Driven Magnetic and Structure Transitions in Superconducting NaFeAs Single Crystals Measured by Angle-Resolved Photoemission Spectroscopy

Abstract

The electronic structure of NaFeAs is studied with angle-resolved photoemission spectroscopy on high quality single crystals. Large portions of the band structure start to shift around the structural transition temperature and smoothly evolve as the temperature lowers through the spin density wave transition. Moreover, band folding due to magnetic order emerges slightly above the structural transition. Our observation provides direct evidence that the structural and magnetic transitions share the same origin and could both be driven by the electronic structure reconstruction in Fe-based superconductors instead of Fermi surface nesting. We did not observe any sign of a gap in the superconducting state, which is likely related to weakened superconductivity in the presence of the spin density wave.

Surface and bulk electronic structures of LaFeAsO studied by angle-resolved photoemission spectroscopy

“…Instead, a band at high binding energies shifts down as much as 25 meV, starting from the structural transition temperature and going through the SDW transition smoothly. This has been observed recently in NaFeAs by the authors, 24 where the fluctuating magnetic order was shown to appear below the structural transition temperature. Our results on LaFeAsO further suggest that the SDW picture established in the 122 and 111 series applies in the 1111 series as well.…”

“…Moreover, no energy gap related to Fermi surface nesting was observed, similar to the case of the 122, 111, and 11 series. [16][17][18][19]24,33 …”

Iron-based superconductors: Magnetism, superconductivity, and electronic structure (Review Article)

“…From experiment, there are both pro and con arguments on this problem. Pro: any time when the FS nesting is good (BFA [29,50,52] and other parent compounds of 122 family [56][57][58], NaFeAs [70,71]), the SDW is present, and when nesting is poor or absent (superconducting BKFA [38,39], BFCA [28,45], BFAP [56], and stoichiometric LiFeAs [62]), there is no magnetic ordering. Con: Fe 1+y Te shows different spin order, see Fig.…”

“…Replacing Fe by either Co or Ni suppresses the magnetism and enhances superconductivity [69]. For ARPES on NaFeAs, see [70,71].…”

The orbital characters of low-energy electronic structure in iron-chalcogenide superconductor K x Fe2−y Se2

“…The insulating parental phase even exhibits certain Mott-insulator signatures, and it is phase separated from the superconducting phase in the K x Fe 2−y Se 2 superconductor at a mesoscopic scale [7,10]. Moreover, angle-resolved photoemission spectroscopy (ARPES) studies have shown that its Fermi surface is consisted of electron pockets only [7,11,12], which is again distinct from most of the iron-based superconductors [13][14][15][16][17]. These unique properties of K x Fe 2−y Se 2 have raised a lot of interest.…”