Spontaneous Symmetry Breaking and Dynamic Phase Transition in Monolayer Silicene

TL;DR

This study reveals a temperature-induced phase transition in monolayer silicene on Ag(111), involving spontaneous symmetry breaking, ultra buckling, and dynamic flip-flop motion, affecting its electronic properties near the Dirac point.

Contribution

It demonstrates the spontaneous symmetry breaking and phase transition in silicene monolayer driven by weak substrate interactions, with insights into electronic structure modifications.

Findings

Phase transition occurs below 40 K to rhombic phases.

Spontaneous ultra buckling induces energy-degenerate phases.

Dynamic flip-flop motion causes high-temperature honeycomb structure.

Abstract

The (r3xr3)R30{\deg} honeycomb of silicene monolayer on Ag(111) was found to undergo a phase transition to two types of mirror-symmetric boundary-separated rhombic phases at temperatures below 40 K by scanning tunneling microscopy. The first-principles calculations reveal that weak interactions between silicene and Ag(111) drive the spontaneous ultra buckling in the monolayer silicene, forming two energy-degenerate and mirror-symmetric (r3xr3)R30{\deg} rhombic phases, in which the linear band dispersion near Dirac point (DP) and a significant gap opening (150 meV) at DP were induced. The low transition barrier between these two phases enables them interchangeable through dynamic flip-flop motion, resulting in the (r3xr3)R30{\deg} honeycomb structure observed at high temperature.