Inter-quintuple layer coupling and topological phase transitions in the chalcogenide topological insulators

TL;DR

This study uses DFT calculations to explore how varying lattice ratios in topological insulators induces phase transitions, highlighting the role of inter-quintuple layer interactions in tuning topological states.

Contribution

It provides a systematic analysis of topological phase transitions driven by lattice ratio changes, emphasizing inter-layer physics in 3D topological insulators.

Findings

Topological phase transitions are controlled by inter-quintuple layer Coulomb and van der Waals interactions.

The materials exhibit stable quintuple layers with quasi-linear behavior near the transition.

Transition mechanisms are clarified without applying hydrostatic pressure.

Abstract

Driving quantum phase transitions in the 3D topological insulators offers pathways to tuning the topological states and their properties. We use DFT-based calculations to systematically investigate topological phase transitions in Bi$_2$Se$_3$, Sb$_2$Se$_3$, Bi$_2$Te$_3$ and Sb$_2$Te$_3$ by varying the $c/a$ ratio of lattice constants. This ensures no net hydrostatic pressure under anisotropic stress and strain and allows a clear identification of the physics leading to the transition. As a function of $c/a$, all of these materials exhibit structural and electronic stability of the quintuple layers (QLs), and quasi-linear behavior of both the inter-quintuple layer distance and the energy gap near the topological transition. Our results show that the transition is predominantly controlled by the inter-QL physics, namely by competing Coulomb and van der Waals interactions between the outer atomic sheets in neighboring quintuple layers. We discuss the implications of our results for topological tuning by alloying.