Anomalous Scaling Enables Lower-Threshold and Ultrafast Switchable Nanolasing in a Phase-Pure Quasi-2D Perovskite Cavity.

Semiconductor micro/nanolasers have been investigated for several decades and hold great potential in bioimaging, high-density storage, and optical communications. Nevertheless, their performance typically declines as the laser cavity size decreases due to reduced mode volume, increased losses, and thermal challenges. Herein, we report an anomalous scaling law in quasi-2D Ruddlesden-Popper perovskite microplates, where smaller cavities exhibit lower thresholds. We identify the origin of this behavior as biexciton lasing dynamics strongly modulated by size-dependent exciton reabsorption. In smaller microcavities, suppressed reabsorption enhances photon recycling, which, in turn, promotes efficient biexciton gain and facilitates a four-level cascade lasing process. This mechanism not only inverts the expected size-performance trend but also enables ultrafast lasing switching on picosecond time scales, as directly probed by transient spectroscopy. These results indicate the critical role of photon reabsorption in tailoring light-matter interactions at the nanoscale and provide a practical strategy for designing high-performance laser sources toward integrated quantum photonics and ultrafast optical computing.