Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi(2)Se(3).
Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi(2)Se(3).
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DOI：
10.1038/ncomms13259
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发表时间：
2016-10-31
影响因子：
16.6
通讯作者：
Kampfrath, Tobias
中科院分区：
文献类型：
--
作者：
Braun, Lukas;Mussler, Gregor;Hruban, Andrzej;Konczykowski, Marcin;Schumann, Thomas;Wolf, Martin;Muenzenberg, Markus;Perfetti, Luca;Kampfrath, Tobias
三维拓扑绝缘体是一种令人着迷的材料，具有绝缘体和金属表面，可容纳具有锁定自旋和动量的高度移动的电荷载流子。值得注意的是，可以使用定制的光束发射方向和大小可调的表面电流。为了更好地理解潜在机制，需要在基本散射事件的时间尺度（∼10 fs）上解决当前的动力学问题。在这里，我们通过对伴随发射的 0.3 至 40 THz 宽带太赫兹 (THz) 电磁场进行采样，以 20 fs 的时间分辨率激发并测量模型拓扑绝缘体 Bi2Se3 中的光电流。引人注目的是，表面电流响应主要是沿 Se-Bi 键的超快电荷转移。相比之下，与基于狄拉克锥体不对称减少的生成场景相比，与光子螺旋度相关的光电流被发现要小几个数量级。我们的研究结果与基于拓扑绝缘体表面电流的宽带光电器件直接相关。 拓扑绝缘体中的表面电流可以通过光控制，但其基本机制尚不清楚。在这里，布劳恩等人。报道了Ca掺杂Bi2Se3表面的超快位移光电流，而注入电流比狄拉克锥体的不对称减少所预期的要小得多。
Three-dimensional topological insulators are fascinating materials with insulating bulk yet metallic surfaces that host highly mobile charge carriers with locked spin and momentum. Remarkably, surface currents with tunable direction and magnitude can be launched with tailored light beams. To better understand the underlying mechanisms, the current dynamics need to be resolved on the timescale of elementary scattering events (∼10 fs). Here, we excite and measure photocurrents in the model topological insulator Bi2Se3 with a time resolution of 20 fs by sampling the concomitantly emitted broadband terahertz (THz) electromagnetic field from 0.3 to 40 THz. Strikingly, the surface current response is dominated by an ultrafast charge transfer along the Se–Bi bonds. In contrast, photon-helicity-dependent photocurrents are found to be orders of magnitude smaller than expected from generation scenarios based on asymmetric depopulation of the Dirac cone. Our findings are of direct relevance for broadband optoelectronic devices based on topological-insulator surface currents. Surface currents in topological insulators can be controlled by light, but the underlying mechanisms are not well understood. Here, Braun et al. report an ultrafast shift photocurrent at the surface of Ca-doped Bi2Se3, whereas injection currents are much smaller than expected from asymmetric depopulation of the Dirac cone.
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