Abstract
The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.
Highlights
The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics
The electronic structure of the iron-based compounds usually consists of hole-like bands near the Brillouin zone centre and electron-like bands near the Brillouin zone corners, leading to proposals that the electron scattering between the hole pockets around the Brillouin zone centre and the electron pockets around the Brillouin zone corners is a viable mechanism for electron pairing in the iron-based superconductors[5,6,7,8,9,10,11]
With the complications of the interface effect and phase separation problem involved in AxFe2 À ySe2 superconductors and superconducting single-layer FeSe/SrTiO3 films, it becomes less straightforward to conclude whether the same effect of Fermi surface topology on superconductivity is operative in all the iron-based superconductors
Summary
There is no indication of Fermi crossing around the G (0,0) point, except that there is a very weak residual signal near the Fermi level Such a Fermi surface topology is very similar to that found in the superconducting single-layer FeSe/SrTiO3 film (Fig. 1e) with a superconducting temperature at B55 K We note that the electron counting in both FeSe11111 and superconducting singlelayer FeSe/SrTiO3 film is much smaller than 0.18 electrons per Fe in AxFe2 À ySe2 superconductor (Fig. 1f)[15,16,17,18] when only considering the M point electron Fermi surface sheet.
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