Auxetic and Ferroelastic Borophane: A Novel 2D Material with Negative Possion's Ratio and Switchable Dirac Transport Channels.

Recently synthesized atomically thin boron sheets (that is, borophene) provide a fascinating template for new material property discovery. Here, we report findings of an extraordinary combination of unusual mechanical and electronic properties in hydrogenated borophene, known as borophane, from first-principles calculations. This novel 2D material has been shown to exhibit robust Dirac transport physics. Our study unveils that borophane is auxetic with a surprising negative Poisson's ratio stemming from its unique puckered triangle hinge structure and the associated hinge dihedral angle variation under a tensile strain in the armchair direction. Our results also identify borophane to be ferroelastic with a stress-driven 90° lattice rotation in the boron layer, accompanied by a remarkable orientation switch of the anisotropic Dirac transport channels. These outstanding strain-engineered properties make borophane a highly versatile and promising 2D material for innovative applications in microelectromechanical and nanoelectronic devices.