The University of Birmingham researchers’ study, published in Nature Communications, provides a significant step toward creating and managing quantum materials with desired novel features that defy conventional physics.
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The material satisfies the conditions of the “Kitaev quantum spin liquid state,” an elusive phenomenon researchers have attempted to understand for decades. It is based on a ruthenium framework.
The materials offer a path to magnetic properties that operate differently from traditional “ferromagnets,” arranged around two poles. Electrons in ferromagnets, such as the well-known bar magnets on refrigerators and noticeboards, interact to behave as small magnets that attract and repel one another. This causes all of the electrons to point in the same direction, which gives the magnet its force.
The magnetic characteristics of liquid materials with quantum spin react differently. These materials are disordered and their electrons connect magnetically through a phenomenon known as quantum entanglement, as opposed to the well-ordered properties of ferromagnets.
Although quantum spin liquids exist in theory and have been simulated by scientists, they have not been produced experimentally or discovered in nature before.
The current study describes the features of a unique ruthenium-based material, which opens up new avenues for investigating these states of matter.
This work is a really important step in understanding how we can engineer new materials that allow us to explore quantum states of matter. It opens up a large family of materials that have so far been underexplored and which could yield important clues about how we can engineer new magnetic properties for use in quantum applications.
Dr Lucy Clark, Associate Professor, School of Chemistry, University of Birmingham
While scientists believe that quantum spin liquid states exist in several naturally occurring copper minerals and mineral crystal systems, this has yet to be proven due to the additional structural complexities seen in nature.
The intricacy of quantum spin liquids also presents challenges for theorists, as modeling produces multiple competing magnetic interactions that are extremely difficult to unravel, producing disagreement among physicists.
Alexei Kitaev, a theoretical physicist, developed a model in 2009 that demonstrated some fundamental principles for quantum spin liquids; however, the magnetic interactions it described required an environment that scientists have been unable to create experimentally without the materials reverting to a conventionally ordered magnetic state.
This phenomenon is assumed to be related to candidate materials' densely packed crystal structures. Since the ions are so close together, they can contact each other directly, causing them to revert to magnetic order.
Using specialist instruments at the UK’s ISIS Neutron and Muon Source and Diamond Light Source, the Birmingham-based team demonstrated that a new material with an open framework structure can adjust the interactions between ruthenium metal ions, opening up a new route to the Kitaev quantum spin liquid state.
Importantly, the magnetic interactions formed within these more open structures are less than they would otherwise be, allowing scientists to fine-tune their precise characteristics.
Dr. Clark concluded, “While this work has not led to a perfect Kitaev material, it has demonstrated a useful bridge between theory in this field and experimentation, and opened up fruitful new areas for research.”
Journal Reference:
Li, A. et. al. (2024) Kitaev interactions through extended superexchange pathways in the jeff=1/2 Ru3+ honeycomb magnet RuP3SiO11. Nature Communications. doi.org/10.1038/s41467-024-53900-3