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TT: Fachverband Tiefe Temperaturen

TT 44: Poster Session Correlated Electrons

TT 44.51: Poster

Thursday, March 17, 2011, 10:00–13:00, P1

Strong Electron Correlations in a Two-Dimensional Electron System on a Surface — •Philipp Höpfner¹, Jörg Schäfer¹, Thomas Schramm¹, Max Herpich¹, Gang Li², Werner Hanke², and Ralph Claessen¹ — ¹Physikalisches Institut, Universität Würzburg — ²Institut für Theoretische Physik und Astronomie, Universität Würzburg

A truly two-dimensional system with strong electron-electron correlation effects can be generated in dilute atomic adlayers on surfaces. An intriguing experimental realization is the Sn/Si(111)-(√3×√3) system. Interestingly, this triangular lattice naturally implies spin frustration. Contrary to the naive expectation of a metallic system, there have been recent indications that it is a Mott insulator at low temperature, based on scanning tunneling spectroscopy (STS) and angle-resolved photoemission (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. We find that Sn/Si(111) shows an apparent low-temperature band gap of order 1 eV. It is retained even at room temperature, yet accompanied by changes in the spectral weight. ARPES reveals a surface state of rather narrow band width, which may be 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.
S. Modesti et al., Phys. Rev. Lett. 98, 126401 (2007).