Experimental energy dispersions for valence and conduction bands of iridium

Using angle-resolved photoemission with synchrotron radiation, we have determined the energy-versus-momentum dispersion relations $E\left(\overrightarrow{\mathrm{k}}\right)$ for the valence bands of Ir along the $\Gamma \Lambda L$ and $\Gamma \Delta X$ symmetry directions. This has been achieved by measuring $h\nu$-dependent normal emission spectra from Ir(111) and metastable unreconstructed Ir(100) (1 × 1) surfaces. Conduction-band critical points at $\Gamma$, $X$, and $L$ are seen as structures in the angle-resolved energy spectrum of secondary electrons. Semiempirical final bands were used to obtain $E$ vs $k$ energy dispersions of the initial bands. A strong resonance was observed for direct transitions at $\Gamma$ from the upper $d$ bands ($E=-1.04\mathrm{}$ eV relative to the Fermi level $E_F$) to an $\mathrm{sp}$-like final-state band at $E=+19.5\mathrm{}$ eV. The lower spin-orbit-split $d$ band ($E=-3.18\mathrm{} \mathrm{and} -4.07\mathrm{}$ eV at $\Gamma$) couples strongly to both a $\mathrm{sp}$-like final-state band and flat $f$-like final-state band (located at $E\simeq +15\mathrm{}$ eV near $\Gamma$). Experimental energy bands are compared with Fermi-surface data and a relativistic-augmented-plane-wave band-structure calculation by Andersen. Surface umklapp scattering is shown to be important for bulk-band emission from the (5 × 1) reconstructed Ir(100) surface.