A system with a complex phase transition: Indium chains on Si(111)

We examined in detail the geometric and electronic structure of thin In cha ins on vicinal Si(lll) surfaces by means of low energy electron diffraction and ultrahigh-resolution photoemission as a function of temperature. Our d ata reveal a transition around T-c = 115 K from a high temperature (4 x 1)- to a low temperature (8 x 2)-phase being reversible with a small hysteresi s of the order 10 K. ARPES spectra exhibit clearly important concomitant ch anges in the electronic band structure near the Fermi surfaces and at the b order of the surface Brillouin zones. We derive the dispersive behavior of the bands involved in the transition in detail and demonstrate that at leas t two surface state bands mn and ms show the opening of a pseudo energy gap on the Fermi surface leaving small but finite spectral weight in the low-t emperature state. We conclude that this transition is probably driven by a similar but more complex mechanism than in a conventional Peierls transitio n.