How chemical pressure affects the fundamental properties of rare-earth pnictides: An ARPES view

Angle-resolved photoelectron spectroscopy, supplemented by theoretical calculations has been applied to study the electronic structure of heavy-fermion material CeFePO, a homologue to the Fe-based high-temperature superconductors, and CeFeAs${}_{0.7}$P${}_{0.3}$O, where the applied chemical pressure results in a ferromagnetic order of the 4$f$ moments. A comparative analysis reveals characteristic differences in the Fe-derived band structure for these materials, implying a rather different hybridization of valence electrons to the localized 4$f$ orbitals. In particular, our results suggest that the ferromagnetism of Ce moments in CeFeAs${}_{0.7}$P${}_{0.3}$O is mediated mainly by Fe 3$d_{xz/yz}$ orbitals, while the Kondo screening in CeFePO is instead due to a strong interaction of Fe 3$d_{3z^2-r^2}$ orbitals.

Figure 1

Overview of ARPES results at $h\nu =121$ eV along the $\overline{\Gamma }$-$\overline{X}$direction of (a) CeFeAs${}_{0.7}$P${}_{0.3}$O at VP and (b) CeFePO at HP.[6] Dashed lines indicate EDCs that are presented in Fig. 2. Insets in (a) and (b) show schematic drawings of the band structure, extracted from the experimental data.

Figure 2

Comparison of the EDC along several cuts of the Brillouin zone. Arabic numbers refer to the dashed lines in Fig. 1. Top: EDC at $\overline{\Gamma }$, middle: Fermi level crossing of band $A$ and $A_1$, respectively, and bottom: cut through the peak along the Fermi level.

Figure 3

(a) Spectral function $f$ of a model band structure roughly reflecting the behavior of band $A$, solved with DMFT method. (b) Magnetization of CeFePO as a function of the applied field perpendicular to the iron plane.