Terahertz Extraordinary Optical Transmission Enhancement in Machine-Learning-Assisted Design Meta-Slit of Ti ₃ C ₂ T _x MXene Nanosheet

Ultrathin Ti 3 C 2 T x MXene nanosheets can approach the intrinsic thin-film absorption limit across the entire terahertz band so as to be significant for terahertz device applications. Innovatively, we tested a terahertz meta-slit with a thickness of 10.2 nm Ti 3 C 2 T x MXene nanosheet and discovered extraordinary optical transmission (EOT) enhancement by machine-learning algorithm. The Drude-Smith model derives the complex conductivity and permittivity of Ti 3 C 2 T x MXenes for numerical simulation. A random forest regressor algorithm (RFRA) is used to map the EOT as a function of the meta-slit length, revealing that two EOT windows exhibit significant frequency shifts and Fano resonance line shapes with an increase in length. The multipole decomposition and photonic band structure show that one EOT window is primarily driven by an electric dipole (ED). It gradually evolves into a flatband with increasing meta-slit length and becomes completely decoupled from the incident terahertz waves around the Γ point in the photonic band structure. The other EOT window is driven by the coupling of a toroidal dipole (TD) and magnetic quadrupole (MQ) and exhibits a continuous dispersion state in the photonic band structure. A photonic bandgap occurs between the two EOT windows, enabling tunable control over terahertz transmission. Our results pave the way for terahertz EOT devices.