Common Fermi Surface Topology and Nodeless Superconducting Gap in K0.68Fe1.79Se2 and (Tl0.45K0.34)Fe1.84Se2 Superconductors Revealed from Angle-Resolved Photoemission Spectroscopy

TL;DR

This study uses high-resolution ARPES to reveal Fermi surface topology and nodeless superconducting gaps in K_0.68Fe_1.79Se_2 and (Tl_0.45K_0.34)Fe_1.84Se_2, suggesting a universal electronic structure in these iron-based superconductors.

Contribution

It demonstrates a consistent Fermi surface topology and nodeless superconducting gaps across different A_xFe_2-ySe_2 compounds, advancing understanding of their superconductivity mechanism.

Findings

Fermi surface includes electron pockets near M and Γ points.

Superconducting gaps are nearly isotropic, ~8-9 meV.

Fermi surface topology aligns with other A_xFe_2-ySe_2 superconductors.

Abstract

We carried out high resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of K_0.68Fe_1.79Se_2 (T_c=32 K) and (Tl_0.45K_0.34)Fe_1.84Se_2 (T_c=28 K) superconductors. In addition to the electron-like Fermi surface near M(\pi,\pi), two electron-like Fermi pockets are revealed around the zone center \Gamma(0,0) in K0.68Fe1.79Se_2. This observation makes the Fermi surface topology of K_0.68Fe_1.79Se_2 consistent with that of (Tl,Rb)_xFe_{2-y}Se_2 and (Tl,K)_xFe_{2-y}Se_2 compounds. A nearly isotropic superconducting gap (\Delta) is observed along the electron-like Fermi pocket near the M point in K_0.68Fe_1.79Se_2 (\Delta\sim 9 meV) and (Tl_0.45K_0.34)Fe_1.84Se_2 (\Delta\sim 8 meV). The establishment of a universal picture on the Fermi surface topology and superconducting gap in the A_xFe_2-ySe_2 (A=K, Tl, Cs, Rb and etc.) superconductors will provide important information in understanding the superconductivity mechanism of the iron-based superconductors.