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SYSD: Symposium SKM Dissertation-Prize 2013

SYSD 1: SKM Dissertation-Prize 2013

SYSD 1.4: Hauptvortrag

Montag, 11. März 2013, 12:45–13:10, H2

Domino Day at Surfaces: An Atomistic Picture of Charge Density Wave Formation at Surfaces — •Simone Wall — Fakultät für Physik und CENIDE, Universität Duisburg-Essen, D-47057 Duisburg — Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr

Ultrafast time-resolved reflection high energy electron diffraction [1] was employed to investigate the dynamics of the Peierls-instability-driven phase transition on the (8×2) In/Si(111) surface. At 20K, far below the critical temperature of 90K, the (8×2)-(4×1) phase transition is electronically driven through weak excitation with a fs-laser pulse and results in a long-lasting super-cooled excited (4×1) phase. This metastable situation, far away from equilibrium, is only accessible through the excitation by the fs-laser pulse. The immediate recovery of the groundstate is hindered by an activation barrier for the motion of the atoms. The recovery of the (8×2) ground state on a timescale of 500ps is then only triggered by adsorbates that act as nucleation seeds - the same way that super-cooled water in a bottle freezes upon the insertion of seeds. With increasing density of pre-existing adsorbates the recovery to the groundstate proceeds much faster. Density functional theory calculations reveal the microscopic scenario of the phase transition, which occurs one-dimensionally along the Indium chains. The surface unit cells fall back into their ground state one at a time, like a row of falling dominoes. The phase front propagates at about 800m/s, comparable to the speed of sound [2]. [1] A. Janzen et al., Surf. Sci. 600, 4094 (2006) [2] S. Wall et al., Phys. Rev. Lett. 109, 186101 (2012)