Figure 4: Electronic structure of LaFeAsO_1−xH_x.

(a–d) Two-dimensional Fermi surface of LaFeAsO_1−xH_x with x=0.08 (a), 0.21 (b), 0.36 (c) and 0.40 (d). The blue arrow represents the nesting vector in the (π π) direction. The contribution of Fe-d_xy and d_yz,zx orbitals are coloured green and pink, respectively²¹. (e) Hydrogen doping dependence of As–Fe–As angle in FeAs₄ tetrahedron (orange circles) and arsenic height h_As from the Fe plane (dark sky-blue diamonds). The angles and h_As are determined from Synchrotron X-ray diffraction measurements at 20 K. The solid lines are as a visual guide. The dashed line denotes the regular tetrahedron angle. (f–i) Band structures of LaFeAsO_1−xH_x with x=0.08 (f), 0.21 (g), 0.36 (h) and 0.40 (i). Insets show close-up views of the low energy region. The contribution of Fe-d_xy and d_yz,zx orbitals are coloured green and pink, respectively. (j) Variation in energy level of relevant Fe 3d bands at Γ point with x. The inset is the band structure of LaFeAsO_0.92H_0.08. The Γ_dxy (filled green inverted triangles) and Γ_anti-dxy (open green triangles) signify the bonding and anti-bonding states, respectively, for a bond primary composed of two Fe d_xy orbitals in a unit cell. Also shown is the energy level of degenerate d_yx,zx band (Γ_dyz,zx indicated by filled pink squares). The solid and dashed lines are as a visual guide. (k–n) Total DOS (solid black line) and partial DOS of d_xy (solid green line) and d_yz,zx (solid pink line) orbitals of LaFeAsO_1−xH_x with x=0.08 (k), 0.21 (l), 0.36 (m) and 0.40 (n). The sum of the partial DOS of d_xy and d_yz,zx orbitals is also shown (dotted blue line).