Computational Insights into Phase Changes in Two-Dimensional Transition Metal Dichalcogenides

Layered van der Waals crystals present an extensive structural phase space of polytype, dimensionality, twist and strain. In addition, charge density wave materials exhibit periodic lattice distortions associated with correlated electronic states. Across this materials class, enhanced coupling between structure and functional properties provides a rich parameter space of electronic, optical and magnetic behaviour. Leveraging phase transitions in these materials presents routes to devices based on controlled, multifunctional switching.<br/><br/>Here, I will discuss these diverse, controllable properties in transition metal dichalcogenides (TMDCs). We have recently exhibited hard ferromagnetism in an intercalated TMDC, with magnetic order persisting down to the two-dimensional limit [1]. We used first principles calculations to identify metastable spin states that are strongly dependent on interlayer separation, suggesting that thermal or strain-based mechanisms are available to control the magnetic properties. In addition, we showed the modulation of electronic properties with phase change in mixed polytype structures exhibiting charge density wave distortions [2].<br/><br/>[1] S. Husremović, C. K. Groschner, K. Inzani, I. M. Craig, K. C. Bustillo, P. Ercius, N. P. Kazmierczak, J. Syndikus, M. Van Winkle, S. Aloni, T. Taniguchi, K. Watanabe, S. M. Griffin, and D. K. Bediako, Journal of the American Chemical Society, <b>144</b> 12167 (2022).<br/><br/>[2] S. Husremović, B. H. Goodge, K. Inzani, M. P. Erodici, A. Mier, S. M. Ribet, K. C. Bustillo, T. Taniguchi, K. Watanabe, C. Ophus, S. M. Griffin, and D. K. Bediako, Nature Communications, <b>14</b>, 6031 (2023).