Valence-band and core-level photoemission spectroscopy of ${\text{LaFeAsO}}_{1-x}{\text{F}}_x$

We have investigated the electronic structure of ${\text{LaFeAsO}}_{1-x}{\text{F}}_x$ $\left(x=0;0.1;0.2\right)$ by angle-integrated photoemission spectroscopy and local-density approximation (LDA)-based band-structure calculations. The valence band consists of a low-energy peak at $E\approx -0.25\text{eV}$ and a broad structure around $E\approx -5\text{eV}$, which are in qualitative agreement with LDA. From the photon-energy dependence of these peaks we conclude that the former derives almost exclusively from $\text{Fe}3d$ states. This constitutes experimental evidence for the strong iron character of the relevant states in a broad window around $E_F$ and confirms theoretical predictions.

Figure 1

(Color online) (a) $h\nu$-dependent photoemission valence-band spectra of LaOFeAs. The arrow marks the point of normalization. The red rectangle is the integration window for the low-energy weight shown in panel (d); the inset shows the near $E_F$ region for $h\nu =15\text{eV}$. Note the small change at $E=0$ which indicates the Fermi edge. (b) Local-density approximation (LDA)-derived orbital resolved DOS (density of states). (c) Atomic photoemission cross section for the relevant orbitals (Ref. 21). (d) Ratio of the $\text{Fe}3d$ and $\text{O}2p$ cross sections from (c) (line) compared to experimental values obtained by integrating the low-energy peak (squares).

Figure 2

(Color online) Doping dependence of the valence band for (a) $h\nu =200$, (b) 150, (c) 95, and (d) 48 eV. The spectra have been normalized to their electron count weighted by the photoemission cross section (see Ref. 23). Insets show expanded views on the low-energy region.

Figure 3

(Color online) Doping-dependent spectra of ${\text{LaFeAsO}}_{1-x}{\text{F}}_x$ with $x=0;0.1;0.2$ for (a) $\text{La}4d$ and (b) $\text{As}3d$. The core levels have been normalized to their integrated intensity. The bars mark the position of the peak maxima. The inset shows the observed peak shifts for $\text{La}4d_{5/2}$ (red squares) and $\text{As}3d_{5/2}$ (green circles). The spectra are offset vertically for clarity.