In the realm of quantum physics and materials science, a trio of researchers from the University of Hong Kong—Jiayu Li, Feng-Ren Fan, and Wang Yao—have unveiled a novel aspect of continuous topological phase transitions (CTPTs). Their work, published in the journal Nature Communications, introduces the concept of “quasisymmetry enrichment” in these transitions, which could have significant implications for understanding and manipulating quantum materials.
Continuous topological phase transitions are phenomena where materials undergo changes in their electronic properties without any energy gap closing in their electronic structure. These transitions are governed by low-energy physics, where certain approximate symmetries, termed quasisymmetries, may emerge. The researchers focused on normal-to-Chern insulator transitions, a type of topological phase transition where a material changes from an ordinary insulator to a Chern insulator, which exhibits a quantum Hall effect without external magnetic fields.
The team identified quasisymmetries in the gapless subspaces of these transitions. These quasisymmetries subdivide CTPTs of the same universality class according to quasisymmetry charges. Universality class refers to the idea that different systems can exhibit the same critical behavior, and quasisymmetry charges are a new way to categorize these behaviors. The researchers found that gapless criticalities with nontrivial charges exhibit regulated phenomena, including intrinsic correlations between charge and pseudospin currents and continuous generalized Hall conductivities. These features are conventionally exclusive to gapped phases, meaning they are typically observed in materials where there is an energy gap between the highest occupied and lowest unoccupied electronic states.
The phenomena arise because quasisymmetry forbids certain matrix elements, rendering the generalized Berry curvature integrable. Berry curvature is a concept in quantum mechanics that describes the geometric properties of the quantum state of a system. By establishing quasisymmetry as a fundamental classifying ingredient, the researchers add a new dimension for understanding the rich landscape of quantum phase transitions.
For the energy sector, this research could have practical applications in the development of topological insulators, which are materials that conduct electricity only on their surface or edges while remaining insulating in their interior. These materials are of great interest for potential applications in quantum computing and spintronics, which is an emerging technology that uses the spin of electrons, rather than their charge, to carry information. Understanding and controlling topological phase transitions could lead to the design of new materials with unique electronic properties, paving the way for innovative energy technologies.
Source: Nature Communications, “Quasisymmetry Enriched Gapless Criticality at Chern Insulator Transitions”
This article is based on research available at arXiv.