Unconventional anisotropic s-wave superconducting gaps of the LiFeAs iron-pnictide superconductor

K Umezawa; Y Li; H Miao; K Nakayama; Z-H Liu; P Richard; T Sato; J B He; D-M Wang; G F Chen; H Ding; T Takahashi; S-C Wang

doi:10.1103/PhysRevLett.108.037002

Unconventional anisotropic s-wave superconducting gaps of the LiFeAs iron-pnictide superconductor

Phys Rev Lett. 2012 Jan 20;108(3):037002. doi: 10.1103/PhysRevLett.108.037002. Epub 2012 Jan 20.

Authors

K Umezawa¹, Y Li, H Miao, K Nakayama, Z-H Liu, P Richard, T Sato, J B He, D-M Wang, G F Chen, H Ding, T Takahashi, S-C Wang

Affiliation

¹ Department of Physics, Tohoku University, Sendai 980-8578, Japan.

PMID: 22400776
DOI: 10.1103/PhysRevLett.108.037002

Abstract

We have performed high-resolution angle-resolved photoemission spectroscopy on Fe-based superconductor LiFeAs (T(c)=18 K). We reveal multiple nodeless superconducting (SC) gaps with 2Δ/k(B)T(c) ratios varying from 2.8 to 6.4, depending on the Fermi surface (FS). We also succeeded in directly observing a gap anisotropy along the FS with magnitude up to ~30%. The anisotropy is fourfold symmetric with an antiphase between the hole and electron FSs, suggesting complex anisotropic interactions for the SC pairing. The observed momentum dependence of the SC gap offers an excellent opportunity to investigate the underlying pairing mechanism.