Researchers Reveal Reality of Lossless Energy Transport in Topological Insulators

Topological insulators raise the hope of being able to achieve lossless energy transport, which is true at extremely low temperatures. However, topological insulators fail to maintain this lossless “magic” at room temperature.

Researchers at Monash University, part of the FLEET Centre, have discovered new insights into the effectiveness of topological insulators, highlighting the significant disparity between their lossless energy transport at ultra-low temperatures and the damaging problems that arise at room temperature.

The study, which was published in Nanoscaleinvestigates why topological insulators face serious challenges in maintaining their functionality in a practical working environment, particularly due to the role of electron-phonon interactions.

Topological insulators, especially two-dimensional (2D) topological insulators, are well known for their unique characteristic of conducting electricity across the boundary/edge while the bulk surface remains electrically insulating.

This unique feature allows unidirectional carrier transport without backscattering, with the electrical resistance induced by diffusion being negligible, giving rise to expectations of dissipation-free carrier transport.

Indeed, at ultralow temperatures, these topological insulators often exhibit dissipationless carrier transport, which is consistent with expectations. However, maintaining this characteristic faces a serious challenge as temperatures increase toward room temperature, where phonons (quanta of lattice vibrations) come into play with the carriers.

The role of electron-phonon interactions

This study provides an in-depth analysis of the carrier-phonon interaction and energy transport in the 2D topological insulator under different temperatures.

The interaction between the electron and the phonon (i.e. electron-phonon interactions) plays a crucial role in the significant increase in electrical resistance observed.

Theoretical modeling revealed that electron-phonon scattering was an important source of backscattering at topological edge states, with the strength of the interactions being strongly correlated with the dispersion of the electronic edge states.

The interactions increase dramatically with temperature and are much stronger in the nonlinearly dispersed edge states of native edges compared to the linearly dispersed edge states of passivated edges, causing significant energy dissipation in the temperature range of 200–400 K.

This study therefore highlights the gap between performance at ultra-low temperature and at practical room temperature.

“Since we considered both linear and nonlinear edge dispersions in this study, our results can be applicable to a diverse range of topological insulators,” said Enamul Haque, lead author of the study.

A better fundamental understanding of the role of electron-phonon scattering at the edges of 2D topological insulators is considered essential to advance future electronics technology based on 2D topological insulators. However, previous work has mainly focused on the surface states of 3D topological insulators and the insulating surfaces of 2D topological insulators.

“Our findings could play a crucial role in advancing the applications of topological insulators in practical electronic devices,” Haque says.

The results of this study can guide the search for new quantum materials or how to overcome existing limitations. By overcoming these room-temperature problems, scientists can make progress in realizing all the potential applications of topological insulators in practical technologies, such as transistors and quantum devices.

“A clear understanding of electron-phonon interactions in topological edge states can help develop strong quantum decoherence in qubits, which could potentially improve the stability and scalability of quantum computers,” said Professor Nikhil Medhekar, principal investigator and chief investigator of FLEET.