Highly optical anisotropy, electronic and thermodynamic properties of the topological flat bands Kagome Nb3Cl8

Abstract

This study showcases the intriguing electronic, optical, and thermodynamic properties of Nb3Cl8, an exceptional class of two-dimensional (2D) crystalline materials renowned for their Kagome structure and an exceptional band arrangement featuring remarkably flat energy bands. Nb3Cl8 was found to be a semiconductor with a narrow bandgap energy of 1.23 eV. Our study reveals pronounced anisotropic behavior in various optical aspects, extending within and perpendicular to the ab-plane. We show a distinctive anisotropy in parameters like the refractive index (4.5 in-plane compared to 2.75 out-of-plane), the optical conductivity (8000 (Ω cm)−1 in-plane compared to 100 (Ω cm)−1 in out-of-plane), and the absorption coefficient (105 cm−1 within the plane as opposed to 104 cm−1 in the out-of-plane direction). In addition, the thermodynamic calculations unveil a transition, distinguished by a Schottky anomaly occurring in the specific heat capacity at approximately 100K which is closely associated with the Néel transition of the Nb3Cl8 compound. The presence of robust interactions among quantum spins within Nb3Cl8 was supported by its low thermal conductivity, ranging from 6 to 0.7 W m−1. K−1. This study not only deepens our comprehension of the optical, electronic, and thermodynamic properties of Nb3Cl8 but also establishes a basis for future innovative technological applications.