Strong nodeless pairing on separate electron Fermi surface sheets in (Tl, K)Fe1.78Se2 probed by ARPES
Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences Beijing 100190, China
2 Department of Physics, Zhejiang University - Hangzhou 310027, China
Accepted: 5 February 2011
We performed a high-resolution angle-resolved photoemission spectroscopy study of the Tl0.63K0.37Fe1.78Se2 superconductor (Tc=29 K). We show the existence of two electron-like bands at the M(π, 0)-point which cross the Fermi level at similar Fermi wave vectors to form nearly circular electron-like Fermi surface pockets. We observe a nearly isotropic ∼8.5 meV superconducting gap (2Δ/kBTc∼7) on these Fermi surfaces. Our analysis of the band structure around the Brillouin zone centre reveals two additional electron-like Fermi surfaces: a very small one and a larger one with kF comparable to the Fermi surfaces at M. Interestingly, a superconducting gap with a magnitude of ∼8 meV also develops along the latter Fermi surface. Our observations are consistent with the s-wave strong-coupling scenario.
PACS: 74.25.Jb – Electronic structure (photoemission, etc.) / 74.70.Xa – Pnictides and chalcogenides / 79.60.-i – Photoemission and photoelectron spectra
© EPLA, 2011