Heat can induce multiple phase transitions in topological insulators, offering a novel, non-structural method to control topological phases
Topological insulators are materials that behave as insulators in their interior but support the flow of electrons along their edges or surfaces. These edge states are protected against weak disorder, such as impurities, but can be disrupted by strong disorder. Recently, researchers have explored a new class of materials known as topological Anderson insulators. In these systems, strong disorder leads to Anderson localization, which prevents wave propagation in the bulk while still allowing robust edge conduction.
The Fermi energy is the highest energy an electron can have in a material at absolute zero temperature. If the Fermi energy lies in a conductive region, the material will conduct; if it lies in a ‘gap’, the material will be insulating. In a conventional topological insulator, the Fermi energy sits within the band gap. In topological Anderson insulators, it sits within the mobility gap rather than the conventional band gap, making the edge states highly stable. Electrons can exist in the mobility gap (unlike in the band gap), but they are localized and trapped. Until now, the transition from a topological insulator to a topological Anderson insulator has only been achieved through structural modifications, which limits the ability to tune the material’s properties.
In this study, the authors present both theoretical and experimental evidence that this phase transition can be induced by applying heat. Heating introduces energy exchange with the environment, making the system non-Hermitian. This approach provides a new way to control the topological state of a material without altering its structure. Further heating prompts a second phase transition, from a topological Anderson insulator to an Anderson insulator, where all electronic states become localized, and the material becomes fully insulating with no edge conduction.
This research deepens our understanding of how disorder influences topological phases and introduces a novel method for engineering and tuning these phases using thermal effects. It also provides a powerful tool for modulating electron conductivity through a simple, non-invasive technique.
Do you want to learn more about this topic?
Interacting topological insulators: a review by Stephan Rachel (2018)
