Strong Correlation Effects in the (3×3) Charge Density Wave Phase of Sn/Ge(111)

Angle resolved photoemission spectra of $\mathrm{Sn}/\mathrm{Ge}\left(111\right)-\alpha$ phase show a transition from a dispersive state at 295 K in the metallic $(\sqrt{3}\times \sqrt{3})$ phase to a state with negligible momentum dispersion in the $(3\times 3)$ charge density wave (CDW) phase at 110 K. A depletion of density of states at the Fermi level is observed in photoemission and electron energy loss spectra at 110 K. These effects and the splitting of the Sn $p_z$ band at 110 K point to correlation effects as the cause of the transition to the CDW state.