Ultrafast atomic diffusion inducing a reversible (23√×23√)R30°↔(3√×3√)R30° transition on Sn/Si(111)∶B

Abstract

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.