Quantum-sized topological insulators/semimetals allow ultrahigh and broadband saturable absorption

Two-dimensional topological insulators/semimetals have just lately attracted a lot consideration. Nevertheless, quantum-sized topological insulators/semimetals with intrinsic traits have by no means been reported earlier than. Herein, we report the high-yield manufacturing of topological insulator (i.e., Bi₂Se₃ and Sb₂Te₃) and semimetal (i.e., TiS₂) quantum sheets (QSs) with monolayer buildings and sub-4 nm lateral sizes. Each linear and nonlinear optical performances of the QSs are investigated. The QS dispersions current exceptional photoluminescence with excitation wavelength-, concentration-, and solvent-dependence. The answer-processed QSs-poly(methyl methacrylate) (PMMA) hybrid skinny movies show distinctive nonlinear saturation absorption (NSA). Notably, Bi₂Se₃ QSs-PMMA allows record-high NSA efficiency with a broadband function. Particularly, the (absolute) modulation depths as much as 71.6 and 72.4% and saturation intensities all the way down to 1.52 and 0.49 MW cm^?2 are achieved at 532 and 800 nm, respectively. Such an outstanding NSA efficiency would significantly facilitate their functions in mode-locked lasers and associated fields.