paper

Observation of an isotropic superconducting gap at the Brillouin zone center of Tl $_{0.63}$ K $_{0.37}$ Fe $_{1.78}$ Se $_{2}$

arXiv:1205.0996 · doi:10.1209/0295-5075/99/67001

Abstract

We performed a high-resolution angle-resolved photoemission spectroscopy study on superconducting (SC) Tl $_{0.63}$ K $_{0.37}$ Fe $_{1.78}$ Se $_{2}$ ( $T_{c} = 29$ K) in the whole Brillouin zone (BZ). In addition to a nearly isotropic $\sim$ 8.2 meV 2-dimensional (2D) SC gap ( $2 I^/ k_{B} T_{c} \sim 7$ ) on quasi-2D electron Fermi surfaces (FSs) located around M $(I ¨ , 0, 0)$ -A $(I ¨ , 0, I ¨ )$ , we observe a $\sim 6.2$ meV isotropic SC gap ( $2 I^/ k_{B} T_{c} \sim 5$ ) on the Z-centered 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-next neighbor exchange interaction in the ferrochalcogenide superconductors.

5 pages, 4 figures

Observation of an isotropic superconducting gap at the Brillouin zone center of Tl0.63​K0.37​Fe1.78​Se2​

Abstract

Observation of an isotropic superconducting gap at the Brillouin zone center of Tl $_{0.63}$ K $_{0.37}$ Fe $_{1.78}$ Se $_{2}$