Dimensional Crossover and Topological Phase Transition in Dirac Semimetal Na3Bi Films
Dimensional Crossover and Topological Phase Transition in Dirac Semimetal Na3Bi Films
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狄拉克半金属 Na3Bi 薄膜中的维度交叉和拓扑相变
DOI：
10.1021/acsnano.9b04933
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发表时间：
2019
期刊：
影响因子：
17.1
通讯作者：
Ying-Shuang Fu
中科院分区：
文献类型：
--
作者：
Huinan Xia;Yang Li;Min Cai;Le Qin;Nianlong Zou;Lang Peng;Wenhui Duan;Yong Xu;Wenhao Zhang;Ying-Shuang Fu
三维拓扑狄拉克半金属材料在减薄到二维几层时，可望具有带隙的狄拉克量子点约束效应，并同时显示出有趣的量子自旋霍尔绝缘体相.然而，三维到二维的交叉和相关的拓扑相变，这是有价值的理解拓扑量子相位，仍然没有探索。在此，我们在石墨烯上合成了高质量的Na 3Bi薄膜，并通过扫描隧道显微镜/光谱结合第一性原理计算系统地表征了其厚度依赖的电子和拓扑性质。我们表明，狄拉克间隙出现在钠铋薄膜，提供光谱证据的三维半金属的二维拓扑绝缘体的空间交叉。重要的是，在具有拓扑非平凡边缘态的三层和四层单层（分别为72和65 meV）上，狄拉克能隙的量级相当大。此外，Na_3Bi薄膜的费米能级可以通过一定的生长工艺进行调节，从而为实现电中性输运提供了一条可行的途径。控制狄拉克能隙打开和电中性的可行性使Na 3 Bi薄膜能够实现本征高温QSH效应，并在拓扑器件中获得潜在的应用。
Three-dimensional (3D) topological Dirac semimetal, when thinned down to 2D few layers, is expected to possess gapped Dirac nodesviaquantum confinement effect and concomitantly display the intriguing quantum spin Hall (QSH) insulator phase. However, the 3D-to-2D crossover and the associated topological phase transition, which is valuable for understanding the topological quantum phases, remain unexplored. Here, we synthesize high-quality Na3Bi thin films with √3 × √3 reconstruction on graphene and systematically characterize their thickness-dependent electronic and topological properties by scanning tunneling microscopy/spectroscopy in combination with first-principles calculations. We demonstrate that Dirac gaps emerge in Na3Bi films, providing spectroscopic evidence of dimensional crossover from a 3D semimetal to a 2D topological insulator. Importantly, the Dirac gaps are revealed to be of sizable magnitudes on three and four monolayers (72 and 65 meV, respectively) with topologically nontrivial edge states. Moreover, the Fermi energy of a Na3Bi film can be tunedviaa certain growth process, thus offering a viable way for achieving charge neutrality in transport. The feasibility of controlling Dirac gap opening and charge neutrality enables realizing intrinsic high-temperature QSH effect in Na3Bi films and achieving potential applications in topological devices.