Half-Auxeticity and Anisotropic Transport in Pd Decorated Two-Dimensional Boron Sheets

If one strains a material along a direction, most materials shrink normal to that direction. Similarly, if you compress the material, it will expand in the direction orthogonal to the pressure. Few materials, those of negative Poisson ratio, show the opposite behavior. Here, we show an unprecedented feature, a material that expands normal to the direction of force regardless if it is strained or compressed. Such behavior, called half-auxeticity, has been found for a borophene sheet stabilized by decorating Pd atoms. Herein, we explore Pd-decorated borophene, identify three stable phases of which one has this peculiar property of half auxeticity. After carefully analyzing stability, mechanical and electronic properties we explore the origin of this very uncommon behavior.