Using the advanced technique of muon spin rotation at the Swiss Muon Source (SmS), researchers at the Paul Scherrer Institute (PSI) have made a groundbreaking discovery in quantum physics. They observed a phenomenon known as time-reversal symmetry breaking (TRS-breaking) at the surface of the Kagome superconductor RbV₃Sb₅ at temperatures up to 175 Kelvin (-98 degrees Celsius). This marks the highest temperature at which TRS-breaking has been observed in Kagome materials, setting a new record and offering a tantalizing prospect for future quantum technologies.
In the realm of quantum mechanics, a temperature of 175 K is relatively high. In the bulk of RbV₃Sb₅, TRS-breaking only occurs at a much lower temperature of around 60 K (-213 degrees Celsius). Observing TRS-breaking at the higher temperature of 175 K is a significant advancement, making it more practical to study and potentially harness this quantum effect.
Time-reversal symmetry (TRS) is a principle in physics stating that the fundamental laws governing a system remain unchanged if time were reversed. In some unique materials, including this Kagome superconductor, this symmetry can be broken, meaning the material behaves differently if time were to run backward. The breaking of TRS is associated with unusual electronic and magnetic behaviors that can result in exotic quantum phases—phenomena that are of immense interest for potential applications in quantum computing and other advanced technologies.
In the Kagome superconductor RbV₃Sb₅, the electrons exhibit a behavior known as charge order under specific conditions. This charge order creates localized magnetic fields that break TRS. These magnetic fields lead to remarkable properties in the material’s electronic and magnetic behavior, making Kagome systems a focus of condensed matter physics. The name “Kagome” originates from a Japanese basket-weaving pattern, consisting of interlaced, corner-sharing triangles. Physicists discovered that when atoms are arranged in this pattern, the electronic structure of the material exhibits unusual quantum properties that are highly sought after in condensed matter physics.
One key property in RbV₃Sb₅ is superconductivity, which activates at temperatures below 2 K, an extremely low temperature even by quantum standards. However, other quantum effects, such as TRS-breaking, can manifest at higher temperatures. These higher-temperature quantum phenomena are more accessible and thus hold greater promise for practical applications.
Beyond the high temperature of TRS-breaking, the discovery reveals another intriguing property: the TRS-breaking effect varies depending on the depth from the surface down into the material’s bulk. This tunable behavior allows for potential control of the material’s quantum properties based on depth, creating new pathways to manipulate electronic and magnetic characteristics at more manageable temperatures. The ability to control such phenomena is a critical step toward real-world applications of quantum technology.
This discovery is part of a larger puzzle in the study of unconventional superconductivity, particularly in materials that display such phenomena at more accessible conditions. The new study is published in Nature Communications, and it adds to a body of research led by physicist Zurab Guguchia and his team, who have been exploring TRS-breaking in Kagome superconductors.
Guguchia’s team previously established a link between TRS-breaking and superconductivity in RbV₃Sb₅. While the current study did not focus on superconductivity directly, the researchers suggest that this property, too, could be tunable with depth—a concept they intend to explore in future experiments.
If the recent findings sound familiar, it’s likely because this research builds on prior discoveries. In 2022, Guguchia’s team made headlines by identifying TRS-breaking charge order in a similar Kagome superconductor, marking a significant breakthrough in the field. Since then, the team has demonstrated how this phenomenon can be tuned under various conditions and shown its relationship to unconventional superconductivity. This latest discovery reinforces the potential of Kagome superconductors and TRS-breaking effects in advancing the field of quantum materials and bringing new, exotic quantum phenomena closer to technological application.
Source: Paul Scherrer Institute