Huber Tito E, Johnson Scott, Konopko Leonid, Nikolaeva Albina, Kobylianskaya Anna, Graf Michael J
Howard University, Washington, DC, 20059, USA.
Academy of Sciences, Chisinau, MD-2028, Moldova.
Sci Rep. 2017 Nov 14;7(1):15569. doi: 10.1038/s41598-017-15476-5.
When electrons are confined in two-dimensional materials, quantum-mechanical transport phenomena and high mobility can be observed. Few demonstrations of these behaviours in surface spin-orbit bands exist. Here, we report the observation of quantized conductance in the surface bands of 50-nm Bi nanowires. With increasing magnetic fields oriented along the wire axis, the wires exhibit a stepwise increase in conductance and oscillatory thermopower, possibly due to an increased number of high-mobility spiral surface modes based on spin-split bands. Surface high mobility is unexpected since bismuth is not a topological insulator and the surface is not suspended but in contact with the bulk. The oscillations enable us to probe the surface structure. We observe that mobility increases dramatically with magnetic fields because, owing to Lorentz forces, spiral modes orbit decreases in diameter pulling the charge carriers away from the surface. Our mobility estimates at high magnetic fields are comparable, within order of magnitude, to the mobility values reported for suspended graphene. Our findings represent a key step in understanding surface spin-orbit band electronic transport.
当电子被限制在二维材料中时，可以观察到量子力学输运现象和高迁移率。目前在表面自旋轨道带中很少有这些行为的相关证明。在此，我们报告了在50纳米铋纳米线的表面带中观察到的量子化电导。随着沿线轴方向的磁场增加，这些纳米线的电导呈现出逐步增加以及热功率振荡，这可能是由于基于自旋分裂带的高迁移率螺旋表面模式数量增加所致。表面具有高迁移率是出乎意料的，因为铋不是拓扑绝缘体，并且表面不是悬空的而是与体相接触。这些振荡使我们能够探测表面结构。我们观察到迁移率随着磁场急剧增加，这是因为由于洛伦兹力，螺旋模式的轨道直径减小，将电荷载流子拉离表面。我们在高磁场下的迁移率估计值在数量级上与报道的悬空石墨烯的迁移率值相当。我们的发现代表了理解表面自旋轨道带电子输运的关键一步。
