Two-dimensional quantum spin Hall (QSH) insulators are a promising material class for spintronic applications based on topologically protected spin currents in their edges. Yet, they have not lived up to their technological potential, as experimental realizations are scarce and limited to cryogenic temperatures. These constraints have also severely restricted characterization of their dynamical properties. Here, we report on the electron dynamics of the novel room-temperature QSH candidate bismuthene after photoexcitation using time- and angle-resolved photoemission spectroscopy. We map the transiently occupied conduction band and track the full relaxation pathway of hot photocarriers. Intriguingly, we observe photocarrier lifetimes much shorter than those in conventional semiconductors. This is ascribed to the presence of topological in-gap states already established by local probes. Indeed, we find spectral signatures consistent with these earlier findings. Demonstration of the large band gap and the view into photoelectron dynamics mark a critical step toward optical control of QSH functionalities.

中文翻译：

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二维拓扑绝缘体铋中的超快动量分辨热电子动力学

二维量子自旋霍尔 (QSH) 绝缘体是一种很有前途的材料类别，可用于基于其边缘的拓扑保护自旋电流的自旋电子应用。然而，由于实验实现稀缺且仅限于低温，它们并没有发挥其技术潜力。这些约束也严重限制了其动力学特性的表征。在这里，我们使用时间和角度分辨光电子能谱报告了光激发后新型室温 QSH 候选铋的电子动力学。我们绘制瞬时占据的导带并跟踪热光载流子的完全弛豫路径。有趣的是，我们观察到光载流子的寿命比传统半导体短得多。这归因于局部探针已经建立的拓扑间隙状态的存在。事实上，我们发现光谱特征与这些早期发现一致。大带隙的演示和对光电子动力学的看法标志着朝着 QSH 功能的光学控制迈出了关键一步。