Thickness-dependent topological phase transition and Rashba-like preformed topological surface states of α-Sn(001) thin films on InSb(001)

K. H. M. Chen^1*, K. Y. Lin², S. W. Lien³, S. W. Huang¹, C. K. Cheng², H. Y. Lin¹, C. H. Hsu⁴, T. R. Chang^3,5,6, C. -M. Cheng^4,7,8, M. Hong², J. Kwo¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan
³Department of Physics, National Cheng Kung University, Tainan, Taiwan
⁴National Synchrotron Radiation Research Center, Hsinchu, Taiwan
⁵Center for Quantum Frontiers of Research and Technology (QFort), Tainan, Taiwan
⁶Physics Division, National Center for Theoretical Sciences, National Taiwan University, Taipei, Taiwan
⁷Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
⁸Taiwan Consortium of Emergent Crystalline Materials, Ministry of Science and Technology, Taipei, Taiwan

* Presenter:K. H. M. Chen, email:s105022804@m105.nthu.edu.tw

Topological materials, possessing a spin-momentum locked topological surface state (TSS), have attracted much interest due to their potential applications in spintronics. α-phase Sn (α-Sn), being one of them, displays enriched topological phases via bandgap engineering through a strain or confinement effect. In this work, we investigated the band evolution of in-plane compressively strained α-Sn(001) thin films on InSb(001) from 3 bilayers (BL) to 370 BL by combining angle-resolved photoemission spectra and first-principles calculations. Gapped surface states evolved to a linearly dispersive TSS at a critical thickness of 6 BL, indicating that the system undergoes a phase transition from topologically trivial to nontrivial. For films thicker than 30 BL, new surface bands were observed and attributed to Rashba-like surface states (RSS). These RSS served as a preformed TSS in another strain-induced topological phase transition. In thick films, 370 BL, α-Sn(001), so as to preclude the confinement effect, our results were consistent with a Dirac semimetal phase with Dirac nodes located along Γ–Z. This study deepens our understanding of topological phase transitions and the evolution of Dirac states. Furthermore, the coexistence of TSS and RSS in a Dirac semimetal α-Sn might significantly enhance the potential for spintronic applications.

Keywords: α-Sn(001), angle-resolved photoemission spectroscopy, Rashba-like surface state, topological phase transition, Dirac semimetal