Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa, 50011, USA.
Department of Physics, University of Notre Dame, Notre Dame, IN, 46556, USA.
Nat Commun. 2019 Feb 5;10(1):607. doi: 10.1038/s41467-019-08559-6.
Topology-protected surface transport of ultimate thinness in three-dimensional topological insulators (TIs) is breaking new ground in quantum science and technology. Yet a challenge remains on how to disentangle and selectively control surface helical spin transport from the bulk contribution. Here we use the mid-infrared and terahertz (THz) photoexcitation of exclusive intraband transitions to enable ultrafast manipulation of surface THz conductivity in BiSe. The unique, transient electronic state is characterized by frequency-dependent carrier relaxations that directly distinguish the faster surface channel than the bulk with no complication from interband excitations or need for reduced bulk doping. We determine the topological enhancement ratio between bulk and surface scattering rates, i.e., γ/γ ~3.80 in equilibrium. The ultra-broadband, wavelength-selective pumping may be applied to emerging topological semimetals for separation and control of the protected transport connected with the Weyl nodes from other bulk bands.
在三维拓扑绝缘体（TI）中，拓扑保护的表面输运正在量子科学和技术领域开辟新天地。然而，如何从体贡献中解缠并选择性地控制表面螺旋自旋输运仍然是一个挑战。在这里，我们使用中红外和太赫兹（THz）光激发专有的内带跃迁，使 BiSe 中的表面太赫兹电导率能够超快速地发生变化。独特的瞬态电子态的特征是依赖于频率的载流子弛豫，这直接区分了比体更快的表面通道，而没有来自带间激发或需要减少体掺杂的复杂性。我们确定了体散射率和表面散射率之间的拓扑增强比，即平衡时γ/γ≈3.80。超宽带、波长选择性的泵浦可应用于新兴的拓扑半金属，以分离和控制与 Weyl 节点相关的受保护传输，同时与其他体带隔离。
