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Strong electron-electron correlation effects in a truly two-dimensional (2D) system can be generated in dilute atomic adlayers systems on surfaces. An intriguing experimental representative is the Sn/Si(111) system with a (√3x√3) surface reconstruction. Such triangular lattice naturally implies spin frustration. Contrary to the naive expectation of the system to be metallic, there have been recent indications that it is a Mott insulator at low temperature, based on scanning tunneling spectroscopy (STS) and angle-resolved photoelectron spectroscopy (ARPES) [1]. However, spectral weight and temperature-dependent changes are largely not understood yet. Here we present new data on this system from both STS and ARPES investigations. We find that Sn/Si(111) remains insulating at room temperature with an apparent band gap of order 1eV, accompanied by changes in the spectral weight. ARPES reveals an occupied surface state with a rather narrow band width, which is attributed to the lower Hubbard band. In comparison to recent advances in theoretical treatments of the triangular lattice, e.g., by dynamical mean field theory, the general trend of the findings can be reproduced, and implications for potential antiferromagnetic order at the surface are discussed. [1] S. Modesti et al., Phys Rev. Lett. 98, 126401 (2007). |
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