Reviewed by Lexie CornerDec 2 2024
Researchers at Loughborough University have made progress in understanding how to fine-tune the behavior of electrons in quantum materials, according to a study published in Nature Communications.
(a) A top-down view of a single layer of Sr2RuO4, the blue square highlights the slight rotations of RuO6 octahedra at the surface of the material. (b) A 3D visualization showing how rotated RuO6 octahedra result in changes of the electron energy bands at the surface of the material, with a higher-order Van Hove singularity (HOVHS) occurring at the middle point. Images taken from the Nature paper. Image Credit: Loughborough University
Superconductivity and magnetism, found in quantum materials like strontium ruthenates and bilayer graphene, have the potential to impact fields such as energy storage and computation.
However, these materials are not yet widely used in real-world applications due to challenges in understanding the complex behavior of their electrons, which carry electrical charge.
In quantum materials, electrons interact strongly and intricately, often losing their individual identities and cooperating in complex, unexpected ways.
While these interactions contribute to the unique properties of quantum materials, they also make them highly sensitive to external factors such as temperature, pressure, or magnetic fields, which can lead to significant and unpredictable changes in their behavior.
Researchers are working to better understand and manage electron interactions to unlock the full potential of quantum materials for next-generation technologies.
One promising approach involves Van Hove singularities (VHs), which are specific points in a material’s band structure.
The band structure acts as a map, showing where electrons can flow and how fast they can travel within a material. VHs are areas on this map where electrons accumulate, creating regions that are highly sensitive to environmental changes.
High-order Van Hove singularities (HOVHS) are a specific type of VH that is particularly of interest to researchers due to their sensitivity to small changes.
Scientists are keen to understand how HOVHs can be used to fine-tune the properties of materials.
However, knowledge of HOVHs remains limited, particularly in terms of identifying where they occur in materials and the factors that contribute to their formation.
Theoretical physics plays a crucial role in advancing research in this area, and researchers at Loughborough have made notable progress with their approach to detecting and analyzing HOVHs.
The method, developed by a team led by Professor Joseph Betouras, is based on the Feynman-Hellmann theorem, a principle in quantum mechanics that examines how energy in a system changes when specific parameters are altered.
The researchers demonstrated their method using strontium ruthenate (Sr₂RuO₄), a well-known metal with complex electronic properties.
By combining theoretical and computational modeling with experimental data from the University of St Andrews, the team identified and analyzed HOVHs, revealing how structural variations at the material's surface lead to the formation of HOVHs that do not appear in the bulk material.
HOVHs are present only on the surface of strontium ruthenate due to slight rotations in its structural units, the ‘RuO₆ octahedra.’
Building on these findings, the researchers made theoretical predictions on how changes to the surface structure could alter the nature of HOVHs. These insights may apply not only to strontium ruthenate but also to other quantum materials.
The team suggests that future experimental studies should focus on testing these predictions through structural modifications, which could help validate the method and potentially guide the design of advanced quantum materials for next-generation electronic technologies.
This research area can be thought of as equivalent to engineering and design in the world of quantum materials. Thanks to our research, it is now possible to envision methods to create these types of singularities to alter the material’s electronic and magnetic properties. This could, for example, enable the creation of superconductors—materials where electrons flow without resistance—at temperatures approaching room temperature.
Joseph Betouras, Professor, Loughborough University
Dr. Anirudh Chandrasekaran, the lead author of the Nature Communications study, added, “This paper introduces a new set of tools to engineer structures with higher-order Van Hove singularities in quantum materials. This could enable phenomena such as superconductivity and magnetism with greater efficiency. This work will, therefore, aid in the discovery of novel materials for technological applications.”
The Loughborough researchers intend to expand on this research by investigating the occurrence of superconductivity near higher-order Van Hove singularities, among other things.
Journal Reference:
Chandrasekaran, A. et. al. (2024) On the engineering of higher-order Van Hove singularities in two dimensions. Nature Communications. doi.org/10.1038/s41467-024-53650-2