Direct Synthesis of Atomically Smooth Epitaxial PbI₂ Nanosheets for Low-Threshold Monolithic Spin Lasers

Spin lasers, boasting strong coherent radiation and spin-encoded information, show great potential in optical information processing and high-speed, secure optical communication. However, conventional spin lasers typically require integration with photonic microcavities, resulting in complex fabrication processes and high costs. Here, we introduce a novel strategy to miniaturize spin lasers by directly synthesizing epitaxial PbI₂ single-nanosheets. These nanosheets exhibit significantly enhanced spin and exciton features and possess atomically smooth surfaces, which greatly improve spontaneous-emission coupling and achieve a low-threshold lasing. As a result, monolithic spin lasing both with a high degree of polarization and record-low-threshold is demonstrated. Theoretical analysis and numerical simulations highlight the importance of the low threshold. Compact monolithic spin lasers with low threshold make them a highly promising candidates for reduced-dimension applications, such as on-chip photonic systems integration and weight-critical scenarios.