Crystal structure, electronic band structure and thermal stability of α-Sn on InSb(111)B

Keng-Yung Lin^1*, 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, email:f02222024@ntu.edu.tw

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 k_z 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