Multiferroicity and giant in-plane negative Poisson’s ratio in wurtzite monolayers

Monolayers of layered materials, such as graphite and molybdenum dichalcogenides, have been the focus of materials science in the last decades. Here, we reveal benign stability and intriguing physical properties in the thinnest monolayer wurtzite ( wz ) semiconductors, which can be exfoliated from their bulk and stacked to reform the wz crystals. The candidate ZnX and CdX (X = S, Se, Te) monolayers possess low cleavage energy and direct bandgaps, which harbor strongly coupled ferroelectricity and ferroelasticity with low transition barriers, giant in-plane negative Poisson’s ratio, as well as giant Rashba spin splitting, enabling the co-tunability of spin splitting and auxetic magnitudes via multiferroic switching. These wz monolayers can be used as building blocks of devices structures, due to their inherent “self-healable” capacity, which offer more flexibility for semiconductor fabrication and provide a natural platform to probe the interplay of multiple physical effects, bringing light into the rich physics in tetrahedral semiconductors.