Volume 99, Number 6, September 2012
|Number of page(s)||5|
|Section||Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties|
|Published online||14 September 2012|
Observation of an isotropic superconducting gap at the Brillouin zone centre of Tl0.63K0.37Fe1.78Se2
1 Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences Beijing 100190, China
2 Paul Scherrer Institut, Swiss Light Source - CH-5232 Villigen PSI, Switzerland
3 Centre de Physique Théorique, Ecole Polytechnique, CNRS - F-91128 Palaiseau Cedex, France, EU
4 Helmholtz-Zentrum Berlin, BESSY - D-12489 Berlin, Germany, EU
5 Department of Physics, Zhejiang University - Hangzhou 310027, China
Received: 27 August 2012
Accepted: 27 August 2012
We performed a high-resolution angle-resolved photoemission spectroscopy study on superconducting (SC) Tl0.63K0.37Fe1.78Se2 (Tc = 29 K) in the whole Brillouin zone (BZ). In addition to a nearly isotropic ∼8.2 meV 2-dimensional (2D) SC gap (2Δ/kBTc ∼ 7) on quasi-2D electron Fermi surfaces (FSs) located around M(π,0,0)-A(π,0,π), we observe a ∼6.2 meV isotropic SC gap (2Δ/kBTc ∼ 5) on the Z-centred electron FS that rules out any d-wave pairing symmetry and rather favors an s-wave symmetry. All isotropic SC gap amplitudes can be fit by a single-gap function derived from a local strong-coupling approach suggesting an enhancement of the next-nearest neighbor exchange interaction in the ferrochalcogenide superconductors.
PACS: 74.70.Xa – Pnictides and chalcogenides / 74.25.Jb – Electronic structure (photoemission, etc.) / 79.60.-i – Photoemission and photoelectron spectra
© EPLA, 2012
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