We studied the band structure of $\mathrm{Nd}\mathrm{Fe}{\mathrm{As}}_{1-x}{\mathrm{P}}_x{\mathrm{O}}_{0.9}{\mathrm{F}}_{0.1}$ ($x=0$, 0.2, 0.4, and 0.6) using angle-resolved photoemission spectroscopy (ARPES) measurements. Two of the hole bands, ${\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}}_1$ $(d_{xz})$ and ${\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}}_3$ $(d_{z^2})$, were observed at the Brillouin zone center in the $P$-polarized light configuration, while the other two hole bands, ${\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}}_2$ $\left(d_{yz}\right)$ and γがんま $(d_{xy})$, were observed in the $S$-polarized alternative. The observed γがんま band shifts downward as $x$ increases, which is consistent with the theoretical prediction for the change in bond angle of As/P-Fe-As/P. Furthermore, a small amount of the $d_{xy}$ orbital component was observed at the same binding energy as that of the top of the ${\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}}_1$ band, thus indicating the band reconstruction of the originally degenerate ${\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}}_1$ and ${\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}}_2$ $(d_{xz}/d_{yz})$ bands by the unoccupied $d_{xy}$ band. The change in the energy level of the ${\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}}_1$ band top with $d_{xy}$ orbital character is accompanied by a $T_{\mathrm{c}}$ upturn at $0.2<x<0.4$. The $T_{\mathrm{c}}$ continues to increase as the ${\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}}_1$ band shifts downward, crossing the Fermi level. The incipient band with the $d_{xy}$ orbital character on its top could be an important ingredient for high $T_{\mathrm{c}}$ 1111-type iron-based superconductors.

• Received 7 May 2020
• Revised 10 April 2022
• Accepted 14 April 2022

DOI:https://doi.org/10.1103/PhysRevB.105.205106