Researchers from the University of Regensburg, including Jan Skolimowski, Nguyen Minh Nguyen, Giuseppe Cuono, Carmine Autieri, and Wojciech Brzezicki, have recently published a study in the journal Physical Review B, exploring the unique topological properties of alpha-tin ($α$-Sn) under strain and its potential implications for the energy sector.
The team developed a tight-binding model for cubic $α$-Sn based on density functional theory (DFT) calculations. They incorporated a variable bond angle into the model to simulate the effects of in-plane strain. In the bulk form, they demonstrated the presence of a $\mathbb{Z}_2$ topological invariant and a non-zero mirror Chern number, indicating that $α$-Sn exhibits dual topology—a rare phenomenon where two distinct topological phases coexist.
The researchers then calculated the topological phase diagram of multi-layer $α$-Sn as a function of strain and the number of layers. They found that a non-trivial quantum spin Hall state, which could be useful for spintronic applications, appears only under compressive strain and when the material is at least five layers thick.
Interestingly, the team discovered a variety of edge states with energies within the bulk gap of the system, both in the trivial and non-trivial phases. These states were localized in different positions, such as the side surfaces, top/bottom surfaces, or the hinges of the material. The researchers traced the origin of these states back to a minimal model that supports chiral symmetry and multiple one-dimensional winding numbers, which vary depending on the direction in the Brillouin zone.
For the energy industry, these findings could pave the way for novel applications in spintronics, which leverages the spin of electrons to store and process information more efficiently than traditional electronics. The unique topological properties of $α$-Sn under strain could lead to the development of new materials and devices for energy-efficient computing and data storage, contributing to the overall reduction of energy consumption in the technology sector. Additionally, the understanding of edge states and their behavior under different conditions could inform the design of more robust and efficient materials for various energy applications.
Source: Skolimowski, J., Nguyen, N. M., Cuono, G., Autieri, C., & Brzezicki, W. (2023). Dual topology and edge-reconstruction in $α$-Sn. Physical Review B, 107(8), 085117.
This article is based on research available at arXiv.