Evolution of Fermi Level Crossings versus H Coverage onW(110)

Two-dimensional Fermi contours of clean and hydrogen-induced surface electronic states have been systematically measured vs coverage of H on W(110) using angle-resolved photoemission. We observe a new pair of spin-orbit-interaction-split surface states, whose splitting grows systematically with hydrogen coverage and whose Fermi contours are strongly nested due to their opposing curvatures. Momentum-dependent electronic transitions between these states drive two previously observed anomalous behaviors: The phonon anomalies along $\overline{\Gamma \mathrm{H}}$ and $\overline{\Gamma \mathrm{S}}$ observed with inelastic helium scattering and electron energy loss spectroscopy, and the shifted-upper-layer reconstruction observed by low-energy electron diffraction for coverages greater than 0.5 monolayer.