Nature of electronic states at the Fermi level of metallic $\beta \text{−}\mathrm{Pb}{\mathrm{O}}_2$ revealed by hard x-ray photoemission spectroscopy

The nature of electronic states at the Fermi energy in metallic $\beta \text{−}\mathrm{Pb}{\mathrm{O}}_2$ has been identified by hard x-ray photoemission spectroscopy (HXPS) combined with x-ray emission spectroscopy and density-functional theory calculations. $\mathrm{Pb}6s$ states are strongly enhanced in HXP spectra, allowing us to locate the Fermi level above the top of the valence band. The occupied conduction-band states have significant $\mathrm{Pb}6s$ character, although the major $6s$ contribution to the density of states is found $9\mathrm{eV}$ below the Fermi energy. The enormous potential of HXPS for the study of $s$ states in oxides is emphasized.

Figure 1

(Color online) Total and partial densities of states for $\beta \text{−}\mathrm{Pb}{\mathrm{O}}_2$ derived from band-structure calculations following convolution with a $0.8\mathrm{eV}$ Gaussian broadening function (see text). The inset shows the unbroadened full density of states. Energies are given relative to the Fermi energy for stoichiometric $\beta \text{−}\mathrm{Pb}{\mathrm{O}}_2$.

Figure 2

(a) O $K$ shell x-ray emission spectrum of $\beta \text{−}\mathrm{Pb}{\mathrm{O}}_2$. (b) HXPS excited at $h\nu =6000\mathrm{eV}$ (solid line) with data at $h\nu =1486.6\mathrm{eV}$ taken from Ref. 11 superimposed (dotted line). (c) Cross-section weighted densities of states derived from cross sections given in Ref. 16 at $h\nu =6000\mathrm{eV}$ (solid line) and $1486.6\mathrm{eV}$ (dotted line). The Fermi level has been set $1.6\mathrm{eV}$ above the valence-band maximum to facilitate comparison with experimental data. (d) HXPS excited at $h\nu =7700\mathrm{eV}$.