Department of Physics, Massachusetts Institute of Technology, Cambridge, 02139, USA.
Phys Rev Lett. 2011 Aug 12;107(7):077401. doi: 10.1103/PhysRevLett.107.077401. Epub 2011 Aug 10.
Topological insulators possess completely different spin-orbit coupled bulk and surface electronic spectra that are each predicted to exhibit exotic responses to light. Here we report time-resolved fundamental and second harmonic optical pump-probe measurements on the topological insulator Bi(2)Se(3) to independently measure its photoinduced charge and spin dynamics with bulk and surface selectivity. Our results show that a transient net spin density can be optically induced in both the bulk and surface, which may drive spin transport in topological insulators. By utilizing a novel rotational anisotropy analysis we are able to separately resolve the spin depolarization, intraband cooling, and interband recombination processes following photoexcitation, which reveal that spin and charge degrees of freedom relax on very different time scales owing to strong spin-orbit coupling.
拓扑绝缘体具有完全不同的自旋轨道耦合体相和表面电子谱，它们各自被预测会对光表现出奇特的响应。在这里，我们报告了拓扑绝缘体 Bi(2)Se(3) 的时间分辨基频和二次谐波光泵浦探测测量，以独立地测量其体相和表面选择性的光诱导电荷和自旋动力学。我们的结果表明，瞬态净自旋密度可以在体相和表面相中被光诱导，这可能会驱动拓扑绝缘体中的自旋输运。通过利用一种新颖的旋转各向异性分析，我们能够分别解析光激发后自旋去极化、内带冷却和带间复合过程，这表明由于强自旋轨道耦合，自旋和电荷自由度的弛豫时间尺度非常不同。
