Hot biexcitons driven by extreme optical confinement

Xinyi Wang; Kaushik Kudtarkar; Wenjing Wu; Yunjo Jeong; Yuxuan Cosmi Lin; Xiaofeng Qian; Junichiro Kono; Shengxi Huang; Shoufeng Lan

arXiv · 2605.08041

Hot biexcitons driven by extreme optical confinement

Xinyi Wang·Kaushik Kudtarkar·Wenjing Wu·Yunjo Jeong·Yuxuan Cosmi Lin·Xiaofeng Qian·Junichiro Kono·Shengxi Huang·Shoufeng Lan

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Abstract

A powerful means to understanding condensed matter that possesses a multi-constituent, non-isolated, and complex nature, with a preeminent example being two-dimensional (2D) materials, is studying many-body interactions. However, experimentally observing high-order many-body interactions is a daunting task due to its heavy reliance on the abundance of low-order complexes. Here, we report the observation of four-body hot biexcitons in an energetically unfavorable bilayer of tungsten disulfide (WS2) through creating extreme optical confinement. Specifically, we integrate a non-radiative bound state in the continuum (BIC) into a photonic crystal (PhC) defect cavity, forming a quasi-three-dimensional (q-3D) but open confinement for photons at the driving frequency. The extremely confined photons in both reciprocal and physical spaces then excite inherently unproductive two-body hot excitons situated slightly above the indirect bandgap so efficiently that they form overwhelmed higher-order four-body hot biexcitons. Distinctively, these hot biexcitons exhibit substantial valley polarization and coherence at room temperature, which we attribute to the topological nature of BICs and the associated q-3D confinement with an orbital angular momentum. Besides achieving room-temperature biexcitons, the q-3D confinement could be valuable for higher-order interactions, such as triexcitons, and many other many-body phenomena, including Bose-Einstein condensation.

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Xinyi Wang, Kaushik Kudtarkar, Wenjing Wu, Yunjo Jeong, Yuxuan Cosmi Lin, Xiaofeng Qian, Junichiro Kono, Shengxi Huang, Shoufeng Lan. 2026-05-08. Hot biexcitons driven by extreme optical confinement. https://arxiv.org/abs/2605.08041

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