Structural degeneracies arise on unit cells with reduced symmetries that are prevalent in two-dimensional materials beyond graphene. Materials with structural degeneracies develop domains, and these structures can undergo structural transitions that can have a predominant two-dimensional character, provided that there is an energetic path among degenerate structures that is smaller than the melting point. Studies of these 2D phase transitions will be demonstrated on the family of group IV-monochalcogenides [1-5]. I will include results on ultra-thin SnTe that are part of an incipient collaboration with MPI. As a consequence of these transitions, the design of two-dimensional materials must take into account material properties at finite temperature, especially if operation is close to the critical temperature associated with the 2D structural transition. This work of a basic nature has deep consequences for potential applications of these novel materials.
1. Two-dimensional disorder in black phosphorus and monochalcogenide monolayers. M. Mehboudi, A.M. Dorio, W. Zhu, A. van der Zande, H.O.H. Churchill, A.A. Pacheco-Sanjuan, E.O. Harriss, P. Kumar, and S. Barraza-Lopez. Nano Lett. 16, 1704 (2016).
2. Structural phase transition and material properties of few-layer monochalcogenides. M. Mehboudi, B. M. Fregoso, Y. Yang, W. Zhu, A. van der Zande, J. Ferrer, L. Bellaiche, P. Kumar, and S. Barraza-Lopez. Phys. Rev. Lett. 117, 246802 (2016).
3. Photostrictive two-dimensional materials in the monochalcogenide family. R. Haleoot, C. Paillard, M. Mehboudi, B. Xu, L. Bellaiche, and S. Barraza-Lopez. Phys. Rev. Lett. 118, 227401 (2017).
4. Electronic and optical properties of strained graphene and other strained 2D materials: a review. G. G. Naumis, S. Barraza-Lopez, M. Oliva-Leyva, H. Terrones. Rep. Prog. Phys. 80, 096501 (2017).
5. Tuning the ferro- to para-electric transition temperature and dipole orientation of group-IV monochalcogenide monolayers. S. Barraza-Lopez, T. P. Kaloni, S. P. Poudel, P. Kumar. arXiv:1709.04581 (2017).