Ultrafast Atomic Diffusion Inducing a Reversible (2√3×2√3)R30°↔(√3×√3)R30° Transition on Sn/Si(111)∶B

Dynamical phase transitions are a challenge to identify experimentally and describe theoretically. Here, we study a new reconstruction of Sn on silicon and observe a reversible transition where the surface unit cell divides its area by a factor of 4 at 250 °C. This phase transition is explained by the 24-fold degeneracy of the ground state and a novel diffusive mechanism, where four Sn atoms arranged in a snakelike cluster wiggle at the surface exploring collectively the different quantum mechanical ground states.
This work was supported by the French Agence Nationale de la Recherche (ANR) under Contract SurMott, No. NT-09-618999, and by Spanish Ministerio de Economía y Competitividad, Project No. MAT2014-59966-R.