Collins James L, Tadich Anton, Wu Weikang, Gomes Lidia C, Rodrigues Joao N B, Liu Chang, Hellerstedt Jack, Ryu Hyejin, Tang Shujie, Mo Sung-Kwan, Adam Shaffique, Yang Shengyuan A, Fuhrer Michael S, Edmonds Mark T
School of Physics and Astronomy, Monash University, Clayton, Victoria, Australia.
Monash Centre for Atomically Thin Materials, Monash University, Clayton, Victoria, Australia.
Nature. 2018 Dec;564(7736):390-394. doi: 10.1038/s41586-018-0788-5. Epub 2018 Dec 10.
The electric-field-induced quantum phase transition from topological to conventional insulator has been proposed as the basis of a topological field effect transistor. In this scheme, 'on' is the ballistic flow of charge and spin along dissipationless edges of a two-dimensional quantum spin Hall insulator, and 'off' is produced by applying an electric field that converts the exotic insulator to a conventional insulator with no conductive channels. Such a topological transistor is promising for low-energy logic circuits, which would necessitate electric-field-switched materials with conventional and topological bandgaps much greater than the thermal energy at room temperature, substantially greater than proposed so far. Topological Dirac semimetals are promising systems in which to look for topological field-effect switching, as they lie at the boundary between conventional and topological phases. Here we use scanning tunnelling microscopy and spectroscopy and angle-resolved photoelectron spectroscopy to show that mono- and bilayer films of the topological Dirac semimetal NaBi are two-dimensional topological insulators with bulk bandgaps greater than 300 millielectronvolts owing to quantum confinement in the absence of electric field. On application of electric field by doping with potassium or by close approach of the scanning tunnelling microscope tip, the Stark effect completely closes the bandgap and re-opens it as a conventional gap of 90 millielectronvolts. The large bandgaps in both the conventional and quantum spin Hall phases, much greater than the thermal energy at room temperature (25 millielectronvolts), suggest that ultrathin NaBi is suitable for room-temperature topological transistor operation.
电场诱导的从拓扑绝缘体到传统绝缘体的量子相变已被提议作为拓扑场效应晶体管的基础。在该方案中，“开”状态是电荷和自旋沿着二维量子自旋霍尔绝缘体的无耗散边缘的弹道输运，而“关”状态是通过施加电场产生的，该电场将奇异绝缘体转变为没有导电通道的传统绝缘体。这种拓扑晶体管对于低能耗逻辑电路很有前景，这将需要具有传统和拓扑带隙且远大于室温下热能的电场开关材料，其带隙要比目前所提议的大得多。拓扑狄拉克半金属是寻找拓扑场效应开关的有前景的体系，因为它们处于传统相和拓扑相的边界。在这里，我们使用扫描隧道显微镜和光谱以及角分辨光电子能谱来表明，拓扑狄拉克半金属NaBi的单层和双层薄膜是二维拓扑绝缘体，由于在没有电场的情况下的量子限制，其体能带隙大于300毫电子伏特。通过用钾掺杂或通过扫描隧道显微镜尖端的接近来施加电场时，斯塔克效应完全关闭带隙，并将其重新打开为90毫电子伏特的传统带隙。传统相和量子自旋霍尔相中的大带隙，远大于室温下的热能（25毫电子伏特），这表明超薄NaBi适用于室温拓扑晶体管操作。
