Correlation in low-dimensional electronic states on metal surfaces

We investigate quasi-one-dimensional (quasi-1D) surface states on metals as a well-defined model system for the study of correlation effects by angle-resolved photoemission. Both dimensionally constrained Shockley and Tamm states are examined, the former on the striped O/Cu(1 1 0) phase, the latter on Pt(1 1 0) with and without adsorbates. We observe an unusual change in photoemission intensity of quasi-particle peaks as a function of temperature or adsorbate coverage, which is very similar to ARUPS results on layered systems, Kondo systems, Mott-insulator systems and high-T_c superconductors. The intensity change of the quasi-particle peak is interpreted in terms of a coherent–incoherent transition of the quasi-1D states. For the Tamm states on Pt(1 1 0), we also find other typical fingerprints of correlation such as a kink in the dispersion and a significant mass renormalization close to E_F. A saddle point at the Fermi level provides a large density of states. Therefore, it is reasonable to expect that this quasi-1D surface resonance is involved in surface phase transitions. The results support our previous report about a surface charge-density-wave-induced phase transition on Br/Pt(1 1 0).