Many-body effects and excitonic corrections in the optical response of two-dimensional metallic MXenes

Describing the electronic and excitonic properties of two-dimensional metallic materials is challenging due to the reduced dielectric screening, which enhances many-body interactions and influences the optical response. In this work, we present a comprehensive study of many-body effects on the optical properties of two-dimensional (2D) metallic MXenes—a large family of emerging layered materials with significant potential for optoelectronic, sensing, and energy-harvesting applications. Using state-of-the-art methods, we explicitly treat intraband transitions and make use of a full frequency description of the screened Coulomb interaction, two aspects that are particularly important when treating many-body effects in metals. Our results reveal that many-body effects substantially modify the band structures of these metallic monolayers, reflecting the limited screening characteristic of atomically thin systems. The GW corrections lead to pronounced changes in the absorption spectra already at the independent-particle level. In contrast, the inclusion of electron-hole interactions through the Bethe-Salpeter equation (BSE) produces comparatively smaller modifications, which we attribute to the finite density of states at the Fermi level in these metallic systems. Overall, our findings highlight the necessity of explicitly accounting for many-body interactions to achieve reliable predictions of the optical properties of 2D metallic materials, and they establish key design principles for MXene-based optoelectronic applications.