Observation of the bands with $d_{xy}$ orbital character near the Fermi level in NdFeAs${}_{1-x}$P${}_x$O${}_{0.9}$F${}_{0.1}$ using angle-resolved photoemission spectroscopy

Abstract

We studied the band structure of NdFeAs${}_{1-x}$P${}_x$O${}_{0.9}$F${}_{0.1}$ ($x$ = 0, 0.2, 0.4 and 0.6) using angle-resolved photoemission spectroscopy (ARPES) measurements. Two of the hole bands, ${\alpha }_1$ $(d_{xz})$ and ${\alpha }_3$ $(d_{z^2})$, were observed at the Brillouin zone center in the $P$-polarized light configuration, while the other two hole bands, ${\alpha }_2$ $(d_{yz})$ and $\gamma$ $(d_{xy})$, were observed in the $S$-polarized alternative. The observed $\gamma$ band shifts downwards 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 ${\alpha }_1$ band, thus indicating the band reconstruction of the originally degenerate ${\alpha }_1$ and ${\alpha }_2$ $(d_{xz}/d_{yz})$ bands by the unoccupied $d_{xy}$ band. The change in the energy level of the ${\alpha }_1$ band top with $d_{xy}$ orbital character is accompanied by a $T_c$ upturn at $0.2<x<0.4$. The $T_c$ continues to increase as the ${\alpha }_1$ 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 $T_c$ 1111-type iron-based superconductors.

arXiv comment10 pages, 7 figures, Accepted for publication in Phys. Rev. B

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