Two-dome structure in electron-doped iron arsenide superconductors.
Iron arsenide superconductors based on the material LaFeAsO(1-x)F(x) 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 O(2-) with F(-) suppresses these transitions and gives rise to superconductivity with a maximum T(c) of 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 LaFeAsO(1-x)H(x) (x<0.53) and, in addition to the conventional superconducting dome seen in LaFeAsO(1-x)F(x), we find a second dome in the range 0.21<x<0.53, with a maximum T(c) of 36 K at x=0.3. Density functional theory calculations reveal that the three Fe 3d bands (xy, yz and 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 T(c).
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama                 226-8503, Japan.
Soshi
S
Iimura
Satoru
S
Matsuishi
Satoru
S
Matuishi
Hikaru
H
Sato
Taku
T
Hanna
Yoshinori
Y
Muraba
Sung Wng
SW
Kim
Jung Eun
JE
Kim
Masaki
M
Takata
Hideo
H
Hosono
D004553:Electric Conductivity; D058085:Iron Compounds / Q000737:chemistry*
D058085:Iron Compounds