Theory of the two-dimensional paraelectric structural transformation of ferroelectric group-IV monochalcogenide monolayers*

After the initial description of a thermally-driven two-dimensional structural transformation in group-IV monochalcogenide monolayers [1] and its subsequent experimental demonstration [2], an additional publication claimed that the transformation can be determined via a Landau model based on an unidirectional optical phonon mode going soft [3]. In this presentation, we disclose a quadratic dispersion of softening modes and analyze molecular dynamics data to understand the atomistic motions underlying the ferroelectric to paraelectric transformation in these atomically thin membranes. We are then able to characterize a hierarchy of critical temperatures Tc that are dependent on structural constraints. Additional dependencies of Tc on the assumptions used to set interatomic forces are discussed as well [4].

References:
[1] M. Mehboudi et al., Nano Lett. 16, 1704 (2016)
[2] K. Chang et al., Science 353, 274 (2016)
[3] R. X. Fei, W. Kang, L. Yang, PRL 117, 097601 (2016)
[4] J. W. Villanova, P. Kumar, and S. Barraza-Lopez, submitted on September 19, 2019.