Observation of an isotropic superconducting gap at the Brillouin zone center of Tl$_{0.63}$K$_{0.37}$Fe$_{1.78}$Se$_2$

X. -P. Wang; P. Richard; A. van Roekeghem; Y. -B. Huang; E. Razzoli; T. Qian; E. Rienks; S. Thirupathaiah; H. -D. Wang; C. -H. Dong; M. -H. Fang; M. Shi; H. Ding

doi:10.1209/0295-5075/99/67001

arXiv · 1205.0996

Observation of an isotropic superconducting gap at the Brillouin zone center of Tl$_{0.63}$K$_{0.37}$Fe$_{1.78}$Se$_2$

X. -P. Wang·P. Richard·A. van Roekeghem·Y. -B. Huang·E. Razzoli·T. Qian·E. Rienks·S. Thirupathaiah·H. -D. Wang·C. -H. Dong·M. -H. Fang·M. Shi·H. Ding

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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 ($2Δ/k_BT_c\sim7$) on quasi-2D electron Fermi surfaces (FSs) located around M$(π,0,0)$-A$(π,0,π)$, we observe a $\sim 6.2$ meV isotropic SC gap ($2Δ/k_BT_c\sim5$) 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.

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X. -P. Wang, P. Richard, A. van Roekeghem, Y. -B. Huang, E. Razzoli, T. Qian, E. Rienks, S. Thirupathaiah, H. -D. Wang, C. -H. Dong, M. -H. Fang, M. Shi, H. Ding. 2012-09-17. Observation of an isotropic superconducting gap at the Brillouin zone center of Tl$_{0.63}$K$_{0.37}$Fe$_{1.78}$Se$_2$. https://doi.org/10.1209/0295-5075%2F99%2F67001

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