场致离解揭示了体绝缘Bi2Se3纳米带中的激子远程光载流子输运
Field-Induced Dissociation Reveals Excitonic Long-Range Photocarrier Transport in Bulk-Insulating Bi2Se3 Nanoribbons
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中文总结 AI 辅助
研究拓扑绝缘体中光载流子低温长程输运机制，结合扫描光电流显微镜与超快瞬态光电压测量，用横向电场作探针，发现长程光响应由电荷中性相关态而非自由电荷载流子携带。
中文摘要 AI 辅助
拓扑绝缘体中的光激发载流子在低温下表现出异常的长程输运，但其潜在机制仍存在争议。在此，我们使用横向电场作为体绝缘掺Sb的Bi2Se3纳米带中光载流子动力学的鉴别探针，将扫描光电流显微镜（SPCM）与超快瞬态光电压（TPV）测量相结合。SPCM表明，抑制光电流所需的横向电场几乎比使自由载流子偏转所需的电场大50倍，但与预期的激子离解场相当。在12K和低激发通量下的TPV测量表明，光载流子扩散率超过了爱因斯坦关系和测量的漂移迁移率所暗示的值一个多数量级，即使在拟合不确定性的下限也保持这一界限。这些观察结果共同表明，长程光响应不是由自由电荷载流子而是由电荷中性相关态携带。
英文摘要
Photoexcited charge carriers in topological insulators display anomalously long-range transport at cryogenic temperatures, but the underlying mechanism remains under debate. Here we use a transverse electric field as a discriminating probe of photocarrier dynamics in bulk-insulating Sb-doped Bi2Se3 nanoribbons, combining scanning photocurrent microscopy (SPCM) with ultrafast transient photovoltage (TPV) measurements. SPCM shows that suppression of the photocurrent requires a transverse electric field nearly 50 times larger than that needed to deflect free carriers, yet comparable to the expected exciton dissociation field. TPV measurements at 12 K and low excitation fluence reveal that the photocarrier diffusivity exceeds the value implied by the Einstein relation and the measured drift mobility by more than an order of magnitude, a bound that holds even at the lower end of the fitting uncertainty. Together, these observations indicate that the long-range photoresponse is not carried by free charge carriers but by a charge-neutral correlated state.
