Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 52: Nanostructures at surfaces: Wires, tubes

O 52.4: Vortrag

Mittwoch, 16. März 2011, 15:45–16:00, WIL B122

The In/Si(111)-(4×1)/(8×2) surface – A fascinating model system for 1D conductors — •Stefan Wippermann, Simone Sanna, and Wolf Gero Schmidt — Lehrstuhl für Theoretische Physik, Universität Paderborn, D-33095 Paderborn

One-dimensional (1D) electronic systems are currently intensively investigated for both fundamental and technological reasons. The ordered array of In nanowires that self-assembles at the Si(111) surface is an extremely popular model system for such 1D electronic systems. It shows an intriguing temperature-induced metal-insulator (MI) transition below 120K from (4×1) to (8×2) translational symmetry. The low-temperature (LT) ground state of the nanowires as well as the driving force and mechanism of the phase transition remain controversial, however.

Here we present an overview of recent ab initio optical response and free-energy calculations [1] that allow for the unambiguous determination of the ground-state geometry. Soft shear and rotary phonon modes are shown to describe the structural transformation between the LT and the room-temperature (RT) geometry. The MI transition is explained as a triple-band Peierls instability. The phase transition is caused by the subtle interplay between the lower total energy of the insulating (8×2) ground state and the larger vibrational and electronic entropy of the less tightly bound and metallic RT (4×1) phase.
[1] S Wippermann et al. PRL 98, 026105 (2007) + PRL 100, 106802 (2008) + PRL 102, 226805 (2009) + PRL 105, 126102 (2010)