Two-dome structure in electron-doped iron arsenide superconductors

TL;DR

This study introduces hydrogen doping in LaFeAsO superconductors, revealing a second superconducting dome with higher Tc and highlighting the role of Fe 3d band degeneracy in enhancing superconductivity.

Contribution

It demonstrates hydrogen doping as a method to access over-doped regions and uncovers a second superconducting dome with increased Tc in LaFeAsO.

Findings

Discovery of a second superconducting dome with Tc up to 36 K.

Fe 3d band degeneracy correlates with high Tc.

Hydrogen doping extends the phase diagram beyond fluorine doping limits.

Abstract

Iron arsenide superconductors based on the material LaFeAsO1-xFx are characterized by a two-dimensional Fermi surface (FS) consisting of hole and electron pockets yielding structural and antiferromagnetic transitions at x = 0. Electron doping by substituting O2- with F- suppresses these transitions and gives rise to superconductivity with a maximum Tc = 26 K at x = 0.1. However, the over-doped region cannot be accessed due to the poor solubility of F- above x = 0.2. Here we overcome this problem by doping LaFeAsO with hydrogen. We report the phase diagram of LaFeAsO1-xHx (x < 0.53) and, in addition to the conventional superconducting dome seen in LaFeAsO1-xFx, we find a second dome in the range 0.21 < x < 0.53, with a maximum Tc of 36 K at x = 0.3. Density functional theory calculations reveal that the three Fe 3d bands (xy, yz, zx) become degenerate at x = 0.36, whereas the FS nesting is weakened monotonically with x. These results imply that the band degeneracy has an important role to induce high Tc.