Controlling structural phases of Sn through lattice engineering

Topology and superconductivity, two distinct phenomena, offer unique insight into quantum properties and their applications in quantum technologies, spintronics, and sustainable energy technologies. Tin (Sn) plays a pivotal role here as an element because of its two structural phases, alpha-Sn exhibiting topological characteristics and 9-Sn showing superconductivity. Here, we demonstrate precise control of these phases in Sn thin films using molecular beam epitaxy with systematically varied lattice parameters of the buffer layer. The Sn films exhibit either 9-Sn or alpha-Sn phases as the buffer layer's lattice constant varies from 6.10 & Aring; to 6.48 & Aring;, spanning the range from GaSb (like InAs) to InSb. The crystal structures of alpha- and 9-Sn films are characterized by x-ray diffraction and confirmed by Raman spectroscopy and scanning transmission electron microscopy. Atomic force microscopy validates the smooth, continuous surface morphology. Electrical transport measurements further verify the phases: resistance drop near 3.7 K for 9-Sn superconductivity and Shubnikov-de Haas oscillations for alpha-Sn topological characteristics. Density functional theory shows that alpha-Sn is stable under tensile strain and 9-Sn under compressive strain, aligning well with experimental findings. Hence, this study introduces a platform controlling Sn phases through lattice engineering, enabling innovative applications in quantum technologies and beyond.