Figure 1

(Color online) (a) Core-level spectroscopy of ${\text{LaFeAsO}}_{0.9}{\text{F}}_{0.1}$ taken in the SC phase using 110 eV photon energy. The upper right inset shows the measured $T_c$ of our sample. (b) Core-level spectrum from (a) taken at three different photon energies. The spectra are normalized to photon flux and show differing trends in intensity based on orbital character.Reuse & Permissions

Figure 2

(Color online) (a) The VB region from Fig. 1b now normalized to the peak near 5 eV binding energy. This helps distinguish Fe from O orbitals in the VB. (b) VB spectra taken with 50 and 100 eV photon energy. The dashed lines mark the locations of the $\text{La}5p$ and $\text{Fe}3d$ peaks. (c) A cartoon summarizing our proposed assignments of orbital character to different regions of the VB DOS based on the data from (a) and (b) and Fig. 1.Reuse & Permissions

Figure 3

(Color online) Near $E_F$ data taken over a range of photon energies from 50 to 110 eV at $T=20\text{K}$. The blue dotted line indicates the energy scale of the spectral feature 15 meV below $E_F$. The inset symmetrizes the data to remove contributions from the Fermi function. The blue dotted lines indicate the $2\Delta \sim 30\text{meV}$ gap feature which we see at all energies.Reuse & Permissions

Figure 4

(Color online) (a) Higher resolution temperature dependent data taken with 23 eV photon energy. The blue dotted line with arrow indicates the near $E_F$ features noted in Fig. 3 at 15 meV. (b) First derivative taken of the data from (a) symmetrized. The temperature dependent dip near $E_F$ corresponds to the 15 meV feature and this energy scale is, again, marked by the blue dotted line. (c)–(d) Symmetrized data from (a) near $E_F$. In (c), we see the gradual temperature evolution of the 15 meV pseudogap feature until the evolution stops around 90 K. In (d), the temperature increase continues with a second abrupt change in the near $E_F$ DOS line shape between 110 and 135 K. (e) Using phase diagram data from Ref. 35, we take the $T_N$ temperatures (blue dots) which define the SDW phase and extrapolate them (blue line) to determine the potential transition temperature for the SDW phase at doping $x=0.1$ (red line), finding a $T_{\text{SDW}}\sim 90\text{K}$, associating this with (c). This is similarly done for the orthorhombic-tetragonal structure transition temperatures, $T_S$ (yellow dots), to find the potential transition temperature at $x=0.1$, $T_{\text{str}}\sim 120\text{K}$, associating this with (d).Reuse & Permissions