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.