Ultrathin MXene assemblies approach the intrinsic absorption limit in the 0.5–10 THz band

Broadband and efficient terahertz absorbing films are crucial to high-performance terahertz detectors, which are in demand for next-generation wireless communications, astronomy, security screening, medical imaging and so on. Recent studies reported a series of two-dimensional materials for enhanced light absorption in terahertz waves, such as graphene, transition metal dichalcogenides and topological insulators, among others. However, it is still challenging to achieve the intrinsic thin-film absorption limit (50%) across the whole ultrabroad terahertz band. Here we demonstrate that ultrathin 10.2-nm-thick (~ λ /30,000) Ti 3 C 2 T x MXene assemblies can reach the intrinsic thin-film absorption limit across the entire 0.5–10 THz band. Such intriguing phenomena are attributed to the highly concentrated free electrons (~10 21  cm −3 ), short relaxation time (~10 fs) and unique intra- and interflake (hopping) electron transport properties in Ti 3 C 2 T x MXenes. Our results are validated by alternating current impedance theory using the Drude–Smith model, rather than classic direct current impedance matching. We believe that our findings will stimulate more studies of broadband terahertz technologies with MXenes and beyond, providing a route to developing compact, supercontinuum terahertz optoelectronic or photothermoelectric devices.