Physicists at Loughborough University have recently made a significant breakthrough in understanding how to manipulate the behavior of electrons within quantum materials, which could potentially revolutionize technologies like computing, energy storage, and superconductivity. Quantum materials, such as bilayer graphene and strontium ruthenates, are known for their extraordinary properties, including superconductivity and magnetism, which make them ideal candidates for next-generation technologies. However, their complexity—particularly in terms of electron behavior—has hindered their widespread application.
At the core of these challenges is the intricate and often unpredictable behavior of electrons in quantum materials. In traditional materials, electrons can be understood largely as individual entities that carry charge through a conductor, following predictable paths. However, in quantum materials, electrons interact in highly complex ways, sometimes losing their individuality and cooperating in a collective manner that results in novel phenomena. While these interactions lead to remarkable properties, such as superconductivity (where electrons move without resistance) or enhanced magnetism, they also make the materials highly sensitive to external factors like temperature, pressure, and magnetic fields. These sensitivities can cause dramatic shifts in the material’s behavior, adding an element of unpredictability that complicates their practical use.
To unlock the full potential of quantum materials, researchers are focused on improving their understanding of how electrons interact and how these interactions can be controlled. One promising area of investigation centers around Van Hove singularities (VHs), which are critical points within a material’s band structure. The band structure of a material acts as a kind of map that indicates where electrons are allowed to move and how quickly they can travel. VHs are special points in this structure where electrons tend to cluster, creating regions that are particularly sensitive to changes in external conditions, such as temperature or pressure. These singularities are key to understanding the behavior of electrons in quantum materials, as they often correlate with properties like superconductivity and magnetism.
An exciting subset of VHs, known as high-order Van Hove singularities (HOVHS), are of particular interest to scientists because they exhibit an even greater sensitivity to subtle changes in the material’s environment. However, the understanding of HOVHS is still in its infancy. Specifically, researchers have struggled to pinpoint where these singularities occur in materials and to identify the factors that give rise to them. Theoretical physics has been instrumental in advancing research in this area, and the team at Loughborough University, led by Professor Joseph Betouras, has made a remarkable contribution with the development of a new method for detecting and analyzing HOVHS.
The method, which builds on the Feynman-Hellmann theorem—a fundamental principle in quantum mechanics—enables scientists to study how changes in specific parameters influence the energy of a system. The team demonstrated the utility of this approach in a paper published in Nature Communications, titled “On the Engineering of Higher-Order Van Hove Singularities in Two Dimensions.” They applied the method to strontium ruthenate (Sr2RuO4), a well-known material with complex electronic properties. Through a combination of theoretical modeling, computational simulations, and experimental data from the University of St Andrews, the researchers were able to detect and analyze the presence of HOVHS within the material.
The team’s findings revealed that HOVHS are not found uniformly throughout the bulk of strontium ruthenate, but rather are confined to the material’s surface. These singularities arise from slight structural rotations in the material’s building blocks, specifically in the arrangement of RuO6 octahedra—key components that make up the crystal structure of strontium ruthenate. This discovery is important because it suggests that surface modifications could be used to engineer the occurrence of HOVHS, offering a powerful tool for controlling the material’s electronic and magnetic properties.
Building on these insights, the researchers proposed a theoretical model for how structural changes at the surface could influence the nature of HOVHS in quantum materials. This work holds potential not just for strontium ruthenate, but for a wide range of quantum materials that exhibit similar behavior. The researchers suggest that experimental studies should now aim to test these theoretical predictions by engineering such structural modifications, which could lead to breakthroughs in tailoring the properties of quantum materials for specific technological applications.
Professor Joseph Betouras, reflecting on the importance of the study, described this research as “equivalent to engineering and design in the world of quantum materials.” He highlighted that the ability to control and create these singularities could be instrumental in developing materials that exhibit desirable properties such as superconductivity at higher temperatures. Traditional superconductors operate only at extremely low temperatures, but the ultimate goal of this research is to develop materials that could function as superconductors at or near room temperature, which would have a profound impact on technology.
Dr. Anirudh Chandrasekaran, the lead author of the paper, emphasized that the research introduces a novel set of tools for manipulating higher-order Van Hove singularities in quantum materials. He explained that this could significantly enhance the efficiency of phenomena like superconductivity and magnetism, which are of great interest for a wide array of technological applications. The insights gained from this research will help guide the discovery of new materials with properties that are fine-tuned for use in electronics, energy storage, and other cutting-edge technologies.
The team at Loughborough University is already looking ahead, planning to explore the phenomenon of superconductivity in greater detail, especially in relation to the influence of higher-order Van Hove singularities. As quantum materials continue to hold promise for future technologies, the ability to manipulate their properties with precision will be crucial. This breakthrough represents a step toward that goal, offering a theoretical framework that could pave the way for a new era of advanced materials with extraordinary properties. By advancing our understanding of how to control the behavior of electrons in quantum materials, these findings could ultimately lead to more efficient, versatile, and powerful materials for a wide range of applications.
Source: Loughborough University