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

Zhexue Chen; Xinyu Sui; Zhangqiang Li; Yueqi Li; Xinfeng Liu; Yong Zhang

doi:10.1039/d3nh00282a

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

Nanoscale Horiz. 2023 Nov 20;8(12):1686-1694. doi: 10.1039/d3nh00282a.

Authors

Zhexue Chen^{1

2}, Xinyu Sui^{2

3}, Zhangqiang Li^{1

2}, Yueqi Li^{1

2}, Xinfeng Liu^{2

3}, Yong Zhang^{1

2}

Affiliations

¹ CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, P. R. China. zhangyong@nanoctr.cn.
² University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
³ CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, P. R. China.

PMID: 37702034
DOI: 10.1039/d3nh00282a

Abstract

Two-dimensional topological insulators/semimetals have recently attracted much attention. However, quantum-sized topological insulators/semimetals with intrinsic characteristics have never been reported before. Herein, we report the high-yield production of topological insulator (i.e., Bi₂Se₃ and Sb₂Te₃) and semimetal (i.e., TiS₂) quantum sheets (QSs) with monolayer structures and sub-4 nm lateral sizes. Both linear and nonlinear optical performances of the QSs are investigated. The QS dispersions present remarkable photoluminescence with excitation wavelength-, concentration-, and solvent-dependence. The solution-processed QSs-poly(methyl methacrylate) (PMMA) hybrid thin films demonstrate exceptional nonlinear saturation absorption (NSA). Particularly, Bi₂Se₃ QSs-PMMA enables record-high NSA performance with a broadband feature. Specifically, the (absolute) modulation depths up to 71.6 and 72.4% and saturation intensities down to 1.52 and 0.49 MW cm^-2 are achieved at 532 and 800 nm, respectively. Such a phenomenal NSA performance would greatly facilitate their applications in mode-locked lasers and related fields.