α- and β-phases of Sn thin films grown on GaSb(001) surface by molecular beam epitaxy*

Tin (Sn) is known to show distinct phases depending on temperature and pressure. The cubic α-Sn is stable below 13.7 C for bulk (higher for thin films), while tetragonal β-Sn is well known metallic phase present at room temperature and shows superconductivity at 3.7 K. Recently, Sn is gaining interest as a unique and promising candidate because of various topological phases of α-Sn by tuning strain, orientation, and thickness configurations as well as excellent superconducting features of β-Sn for quantum devices. We investigate Sn thin films with different α- and β-phases on GaSb(001) surface using molecular beam epitaxy with active liquid Nitrogen cooling as well as by first-principles calculations. We observed β-Sn(110), β-Sn(001), and α-Sn(110) phases with varying growth temperatures for the same film thickness (40 nm). Transport measurement revealed superconductivity for β-Sn(001) phase whereas no superconductivity and large weak localization-like features were seen down to 0.04 K for β-Sn(110) phase. We also study the crystal structure with temperature-dependent Raman spectroscopy. This work highlights a strong connection among novel electronic phases and structure metastability that is critical for controlling the topological and superconducting nature of Sn.