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We study the electronic structure of HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ (Hg1223 ; T$_{c}$ = 134 K) using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). Resonant valence band PES across the O K-edge and Cu L-edge identify correlation satellites originating in O 2p and Cu 3d two-hole final states, respectively. Analyses using the experimental O 2p and Cu 3d partial density of states show quantitatively different on-site Coulomb energy for the Cu-site (U$_{dd}$ = 6.5$\pm$0.5 eV) and O-site (U$_{pp}$ = 1.0$\pm$0.5 eV). Cu$_{2}$O$_{7}$-cluster calculations with non-local screening explain the Cu 2p core level PES and Cu L-edge XAS spectra, confirm the U$_{dd}$ and U$_{pp}$ values, and provide evidence for the Zhang-Rice singlet state in Hg1223. In contrast to other hole-doped cuprates and 3d-transition metal oxides, the present results indicate weakly correlated oxygen holes in Hg1223., Comment: 11 pages, including supplementary material, added references

We report on new LEED, STM and ARPES studies of alkali/Si(111) previously established as having a Mott insulating ground state at surface. The observation of a strong temperature dependent Franck-Condon broadening of the surface band together with the novel $\sqrt{3}\times\sqrt{3}\to2(\sqrt{3}\times\sqrt{3})$ charge and lattice ordering below 270 K evidence a surface charge density wave (SCDW) in the strong e-ph coupling limit ($g\approx8$). Both the adiabatic ratio $\hbar\omega_0/t\approx0.8$ and the effective pairing energy $V_{eff}=U-2g\hbar\omega_0\approx-800$ $meV$ are consistent with the possible formation of a bi-polaronic insulating phase consisting of alternating doubly-occupied/unoccupied dangling bonds as expected in the Holstein-Hubbard model., Comment: 4 pages, 3 figures. accepted in Physical Review Letters (2009)