Semimetallic features in thermoelectric transport properties of 2H–3R phase niobium diselenide

In two-dimensional van der Waals crystals, the interlayer stacking sequence often leads to a change in crystal symmetry and, thus, new polymorphs, leading to an abundant array of physical properties. In this paper, we report the polymorphic form of 2H–3R–NbSe₂ that exhibits a substantial difference in terms of the gate dependence of semimetallic behavior and Seebeck coefficient, compared to the well-known 2H–NbSe₂ with metallic transport behavior. The semimetallic features of 2H–3R–NbSe₂ indicate the presence of minor carriers, confirmed through theoretical calculations, which is in good agreement with the transport behavior. Our results reveal perspectives for understanding the metastable 2H–3R phase NbSe₂, which is not far from equilibrium, and for engineering the materials necessary for efficient energy harvesting.