Emerging materials for photonics: MXenes and Weyl semimetals

Two emerging material classes, namely, two-dimensional transition-metal carbides and nitrides (MXenes) and Weyl Semimetals (WSMs) offer exciting opportunities for tailorable photonic devices. The designer-like characteristics of MXenes, achievable with the choice of composition, stoichiometry and surface termination, and tunable properties of single crystalline WSMs, realized through the manipulation of surface conditions, lead to impressive tunability of optical properties in both systems. MXenes exhibit diverse optical properties ranging from plasmonic behavior to dielectric-to-metallic transition as well as strong nonlinear response useful for ultrafast applications. In turn, WSMs such as TaAs show high photocurrent generation and strong second-harmonic generation while WTe2 holds a promise for chiral anomaly applications. The manipulation of linear and nonlinear optical response including the epsilon near zero (ENZ) behavior as well as investigation of hybrid plasmonic-MXene and plasmonic-WSM structures open a broad range of applications for these materials in emerging photonics.