Auxetic two-dimensional transition metal selenides and halides*

Auxetic two-dimensional materials provide a promising platform for multiple applications at the nanoscale. Utilizing a hypothesis-based data-driven approach we identify multiple materials with remarkable in-plane auxetic behavior in a family of buckled 2D materials with the stoichiometry MX (M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, and X= Se, Cl, Br, I). The desirable auxetic behavior originates from the interplay between the buckled structure and the weak metal-metal interaction determined by their electronic structures. The Poisson's ratio is sensitive to magnetic order and the amount of uniaxial stress applied. A transition from positive Poisson's ratio to negative Poisson's ratio for a subgroup of MX compounds under large uniaxial stress is predicted.