Realization of an Elemental Topological Dirac Semimetal: α-Sn on InSb(111)

Three-dimensional (3D) topological Dirac semimetals (TDSs) are rare but important as a versatile platform for exploring exotic electronic properties and topological phase transitions. A quintessential feature of TDSs is 3D Dirac fermions associated with bulk electronic states near the Fermi level. Using angle-resolved photoemission spectroscopy, we have observed such bulk Dirac cones in epitaxially grown α-Sn films on InSb(111), the first such TDS system realized in an elemental form. First-principles calculations confirm that epitaxial strain caused by the in-plane lattice mismatch of 0.14% is key to the formation of the TDS phase. A phase diagram as a function of epitaxial strain is established that connects the 3D TDS phase through a singular point of a zero-gap semimetal phase to a topological insulator phase. The nature of the Dirac cone crosses over from 3D to 2D as the film thickness is reduced to a few layers.
In collaboration with Cai-Zhi Xu, Yang-Hao Chan, Yige Chen, Peng Chen, Xiaoxiong Wang, Catherine Dejoie, Man-Hong Wong, Joseph Andrew Hlevyack, Hyejin Ryu, Hae-Young Kee, Nobumichi Tamura, Mei-Yin Chou, Zahid Hussain, and Sung-Kwan Mo