Electronic structure of Sb ultrathin film on Bi(111) with large lattice mismatch

Topological phase transitions have been actively investigated to understand the fundamental properties and to develop applications for spintronics. In this study, we focused on Sb ultrathin films that undergo a topological phase transition by lattice strain. In order to fabricate samples with a lattice constant theoretically predicted to be topologically nontrivial, Sb ultrathin films are prepared on a Bi substrate. The surface structure and electronic states of the Sb/Bi heterostructure were confirmed by the low-energy electron diffraction measurement and angle-resolved photoemission spectroscopy. For 2 and 3 BL Sb films, we demonstrated the possibility of creating well-ordered immiscible ultrathin films of Sb on a Bi substrate and observed a “V”-shaped electronic band, which is significantly different from the electronic state of Bi thin films and freestanding Sb ultrathin films. This suggests that the electronic state of the Sb ultrathin film is affected by the Bi substrate. We propose that the “V”-shaped band originates from a topological phase transition due to expanded lattice constants and band hybridization between Bi and Sb. This heterostructure will provide a new platform for investigating the topological phase transitions and applications.