Evidence of multiple nodeless energy gaps in superconductingBa0.6K0.4Fe2As

Abstract

We report on low-temperature scanning tunneling microscopy and spectroscopy (STM) studies of the electronic structure of single-crystalline Ba 0.6 K 0.4 Fe 2 As 2. Multiple superconducting gaps are observed in the density of states (DOS) and the sizes of the two dominant gaps L and S are 7.6 and 3.3 meV, respectively. The flat bottom of the DOS spectra near zero bias indicates the nodeless feature of the gaps, while the global fitting to the spectra definitely requires the anisotropy. The nodeless gaps with finite anisotropy revealed in our STM data agree well with the expectations of an extended s-wave superconductivity.

Effect of heavy-ion irradiation on superconductivity in Ba0.6K0.4Fe2Salovich1, Kim2, Ghosh3 et al. 2013Phys. Rev. B182210View full textAdd to dashboardCite

“…In each case the BCS expression provided a superior fit to a power law. These gap values are in good agreement with STM [15] and ellipsometry [19] measurements that report with an s +− order parameter for which interband scattering produces midgap states, but not for an s ++ pairing state [4,5]. However, interband scattering (unless it is in the pure unitary limit) should also suppress C…”

“…Measurements were performed on two groups of (nominally) optimally doped single crystal Ba 0.6 K 0.4 Fe 2 As 2 [15]. Irradiation with 1.4 GeV 208 Pb ions was performed at the Argonne Tandem Linear…”

On the structure of the superconducting order parameter in high-temperature Fe-based superconductors

“…This is because for s-wave superconductor at the temperatures below TC the reflectance approaches unity at energies ħ< 2Δ. As a result, a peak at ~ 160 cm −1 (19.8 meV) correlates with the magnitude of the larger superconducting gap L ≈ 10 meV [25][26][27]47]. The smaller gap is beyond the frequency range of our IR measurements.…”

“…No model has got an unambiguous experimental confirmation yet, thus making the main issues still unanswered. For example, the experimentally determined BCS ratio in Ba-122 family varies by a factor of six [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], for a review, see 12,34]. A possible reason is the strong out-of-plane gap anisotropy in k-space which seems to "smear" the gap values obtained in bulk probes, and a sensitivity-to-surface of the superconducting properties.…”

Critical fields and vortex pinning in overdopedBa0.2K0.8Fe2As2

“…However, the nature of the superconducting pairing and the symmetry of the order parameter in these remarkable materials remain rather uncertain. In optimally doped Ba 1-x K x Fe 2 As 2 most experiments suggest an almost isotropic superconducting gap [7][8][9][10]. Pairing is reported to be mediated by spin fluctuations [11], which yields a full superconducting gap of s ± symmetry with opposite signs of the order parameter on the hole Fermi surface sheets centered on the Γ-point of the Brillouin zone and on the electron Fermi surface sheets centered on the X-point.…”