Amorphous Bi$_2$Se$_3$ structural, electronic, and topological nature by first-principles

TL;DR

This study uses first-principles simulations to explore the structural and electronic properties of amorphous Bi$_2$Se$_3$, revealing how disorder affects its topological phase and surface states, with implications for large-scale applications.

Contribution

It provides the first detailed ab initio analysis of amorphous Bi$_2$Se$_3$, highlighting the impact of disorder on its topological properties and surface states.

Findings

Melting reduces the energy gap and increases defect environments.

Topological phase stability is weak against disorder, as shown by the spin Bott index.

Amorphous Bi$_2$Se$_3$ exhibits trivial surface states resembling topological states.

Abstract

Crystalline $\rm Bi_2Se_3$ is one of the most explored three-dimensional topological insulator, with a $0.3\;\rm eV$ energy gap making it promising for applications. Its amorphous counterpart could bring to light new possibilities for large scale synthesis and applications. Using ab initio molecular dynamics simulations, we have studied realistic amorphous $\rm Bi_2Se_3$ phases generated by different processes of melting, quenching, and annealing. Extensive structural and electronic characterizations show that the melting process induces an energy gap decrease ruled by growth of the defective local environments. This behavior dictates a weak stability of the topological phase to disorder, characterized by the spin Bott index. Interestingly, we identify the occurrence of topologically trivial surface states in amorphous $\rm Bi_2Se_3$ that show a strong resemblance with standard helical topological states. Our results and methods advance the search of topological phases in three-dimensional amorphous solids.