Subcycle observation of lightwave-driven Dirac currents in a topological surface band
Subcycle observation of lightwave-driven Dirac currents in a topological surface band
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DOI：
10.1038/s41586-018-0544-x
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发表时间：
2018-10-18
期刊：
影响因子：
64.8
通讯作者：
Huber, R.
中科院分区：
文献类型：
--
作者：
Reimann, J.;Schlauderer, S.;Huber, R.
利用光的载波作为交流偏置可以使电子器件具有光学时钟速率（1）。光波驱动的电流被认为是固体中高次谐波产生（2-6），纳米结构中的电荷传输（7-8），阿秒条纹实验（9-16）和原子分辨率超快显微镜（17-18）所必需的。然而，在传统的半导体和半导体中，电子的有限有效质量和超快散射限制了它们的弹道偏移和速度。拓扑绝缘体的类狄拉克、准相对论能带结构（19-29）可能会解除这些限制，从而开启光波电子学的新时代。为了了解电子的相关复杂运动，对载波驱动电流的全面实验访问至关重要。在这里，我们报告角分辨光电子能谱与子周期时间分辨率，使我们能够直接观察到如何的载波的太赫兹光脉冲加速狄拉克费米子的能带结构的拓扑表面状态的Bi 2 Te 3。当光发射电子的太赫兹条纹追踪表面的电磁场时，狄拉克态的加速导致电子在动量空间中的强烈重新分布。无惯性表面电流受到自旋动量锁定的保护，达到每厘米2安培的峰值密度，弹道平均自由程为数百纳米，为全相干光波驱动的电子设备开辟了一个现实的参数空间。此外，我们的能带结构的亚周期分辨率分析可能会大大提高我们的理解，电子动力学和强场相互作用的固体。
Harnessing the carrier wave of light as an alternating-current bias may enable electronics at optical clock rates(1). Lightwave-driven currents have been assumed to be essential for high-harmonic generation in solids(2-6), charge transport in nanostructures(7-8), attosecond-streaking experiments(9-16) and atomic-resolution ultrafast microscopy(17-18). However, in conventional semiconductors and dielectrics, the finite effective mass and ultrafast scattering of electrons limit their ballistic excursion and velocity. The Dirac-like, quasi-relativistic band structure of topological insulators(19-29) may allow these constraints to be lifted and may thus open a new era of lightwave electronics. To understand the associated, complex motion of electrons, comprehensive experimental access to carrier-wave-driven currents is crucial. Here we report angle-resolved photoemission spectroscopy with subcycle time resolution that enables us to observe directly how the carrier wave of a terahertz light pulse accelerates Dirac fermions in the band structure of the topological surface state of Bi2Te3. While terahertz streaking of photoemitted electrons traces the electromagnetic field at the surface, the acceleration of Dirac states leads to a strong redistribution of electrons in momentum space. The inertia-free surface currents are protected by spin-momentum locking and reach peak densities as large as two amps per centimetre, with ballistic mean free paths of several hundreds of nanometres, opening up a realistic parameter space for all-coherent lightwave-driven electronic devices. Furthermore, our subcycle-resolution analysis of the band structure may greatly improve our understanding of electron dynamics and strong-field interaction in solids.