The appearance of topologically protected spin-momentum locked surface states in topological insulators gives rise to robust room temperature spin currents making them ideal candidates for the realization of spintronic devices. New methods are needed to access and manipulate such currents with timescales that are compatible with modern electronics. Here we reveal that an optically induced long-lived (~10 ns), spin-polarized surface state excitation in topological insulators can be easily tuned in both magnitude and duration. Time-resolved angle-resolved photoemission spectroscopy, together with a quantitative model, reveals the ideal conditions for a surface photovoltage in two different topological insulators. Our model predicts that the reported effects are an intrinsic property of topological insulators, as long as the chemical potential falls within the band gap. This work demonstrates that persistent excited topological surface states are photon-accessible and easily tuned in both magnitude and duration, merging photonics- and spintronics-based devices in the same material.

拓扑绝缘体中受拓扑保护的自旋动量锁定表面状态的出现引起了强劲的室温自旋电流，这使其成为实现自旋电子器件的理想候选者。需要新的方法来以与现代电子设备兼容的时间尺度来访问和操纵这种电流。在这里，我们揭示了拓扑绝缘子中的光诱导长寿命（〜10 ns），自旋极化的表面态激发可以容易地在幅度和持续时间上进行调谐。时间分辨角分辨光发射光谱学和定量模型一起揭示了两种不同拓扑绝缘体中表面光电压的理想条件。我们的模型预测，所报告的影响是拓扑绝缘体的固有属性，只要化学势落在带隙内即可。这项工作表明，持久激发的拓扑表面状态是光子可访问的，并且在幅度和持续时间上都易于调整，将基于光子和自旋电子学的设备合并到同一材料中。