Crystal structure, electronic band structure and thermal stability of α-Sn on InSb(111)B
Keng-Yung Lin1*, Ko-Hsuan Chen2, Chao-Kai Cheng1, Sheng-Wen Huang2, Cheng-Maw Cheng3, Minghwei Hong1, Raynien Kwo2
1Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan
2Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
3National Synchrotron Radiation Research Center, Hsinchu, Taiwan
* Presenter:Keng-Yung Lin,
Research efforts on studying the electronic band structure and the topological phase of α-Sn pseudomorphically grown on InSb have increased substantially recently. Bulk α-Sn is a zero-gap material with an inherent band inversion due to spin-orbit coupling. Interestingly, theoretical calculation revealed a strained-induced gap opening at Γ point for α-Sn, and it could become a topological Dirac semimetal (TDS) or a topological insulator (TI) depending on the type of strain. Experimentally, 30-bilayer (BL) α-Sn on InSb(111)B was claimed to be a 3D TDS by angle-resolved photoemission spectroscopy (ARPES), but the ARPES results were less evident compared to other experimental reports of 3D TDS such as those of Na3Bi. In this work, α-Sn thin films were grown on InSb(111)B by molecular beam epitaxy (MBE) with epitaxial InSb layers as the starting surfaces prepared in the same MBE chamber. Single-crystal α-Sn(111) thin films with smooth surfaces and excellent crystallinity were characterized by in-situ reflection high-energy electron diffraction during the MBE growth, and later by atomic force microscopy and X-ray diffraction. Their band structures were studied by ARPES. Much clearer band dispersions around the Fermi level were observed for our 30-BL films, compared to those reported in the literature, with virtually no kz dependence over a series of photon energy for the claimed 3D Dirac state. Furthermore, we have identified another 2D like linear band around the Fermi level with a higher Fermi velocity. Our results, therefore, do not support the 3D TDS phase of 30-BL α-Sn on InSb(111)B observed in the previous experimental work. We have also studied the thermal stability of the α-Sn layer and the heterointerface by annealing a sample under ultra-high vacuum up to 120 ℃. The mirror-like wafer surface indicated no occurrence of phase transition from α-Sn to β-Sn, and the ARPES spectrum remained alike. No increased amount of Sb and In diffusions from InSb into the α-Sn layer examined by core-level photoemission suggests the intactness of the heterostructure.

Keywords: a-Sn, Topological materials, Angle-resolved photoemission spectroscopy