Softening phonon modes drive the structural phase transition in silicene*

Silicene, a silicon analogue of graphene which itself possesses linear electronic band dispersion near the Fermi level, has garnered much interest for its promise of integration in existing electronics technology. Silicene has been experimentally grown in a buckled structure which increases the bending rigidity of silicene in comparison to graphene, but the former has less in-plane stiffness than the latter. [1,2] The buckled structure exhibits a two-fold structural degeneracy that gives rise to a structural phase transition at finite temperature. The transition is underpinned by a softening of phonon modes, and we investigate this behavior by the use of molecular dynamics and the velocity autocorrelation sequence to extract the phonon band structure directly without relying on strictly zero-temperature phonon calculations.

[1] R. E. Roman and S. W. Cranford, Comput. Mater. Sci. 82, 50 (2014).
[2] R. Qin, C. Wang, W. Zhu, and Y. Zhang, AIP Adv. 2, 022159 (2012).