Experimental energy dispersions for valence and conduction bands of iridium

Abstract

Using angle-resolved photoemission with synchrotron radiation, we have determined the energy-versus-momentum dispersion relations $E(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$ for the valence bands of Ir along the $\ensuremath{\Gamma}\ensuremath{\Lambda}L$ and $\ensuremath{\Gamma}\ensuremath{\Delta}X$ symmetry directions. This has been achieved by measuring $h\ensuremath{\nu}$-dependent normal emission spectra from Ir(111) and metastable unreconstructed Ir(100) (1 \ifmmode\times\else\texttimes\fi{} 1) surfaces. Conduction-band critical points at $\ensuremath{\Gamma}$, $X$, 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 $\ensuremath{\Gamma}$ from the upper $d$ bands ($E=\ensuremath{-}1.04$ eV relative to the Fermi level ${E}_{F}$) to an $\mathrm{sp}$-like final-state band at $E=+19.5$ eV. The lower spin-orbit-split $d$ band ($E=\ensuremath{-}3.18 \mathrm{and} \ensuremath{-}4.07$ eV at $\ensuremath{\Gamma}$) couples strongly to both a $\mathrm{sp}$-like final-state band and flat $f$-like final-state band (located at $E\ensuremath{\simeq}+15$ eV near $\ensuremath{\Gamma}$). 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 \ifmmode\times\else\texttimes\fi{} 1) reconstructed Ir(100) surface.