Theoretical physicists Dr. Chengkang Zhou and Professor Zi Yang Meng from The University of Hong Kong, along with experimentalists Zhenyuan Zeng and Professor Shiliang Li from the Chinese Academy of Sciences, have discovered a novel quantum state known as a “Dirac Spin Liquid”. This state is characterized by the emergence of quasiparticles, known as Dirac spinons, which have unique characteristics similar to Dirac particles in high-energy physics. The team’s research focused on a material known as YCu3-Br, which exhibits a quantum spin liquid state. The findings could potentially advance our understanding of condensed matter physics and open doors for further exploration into high-temperature superconductivity and quantum information.
Discovery of Novel Quantum State: The Dirac Spin Liquid
A recent collaboration between theoretical physicists Dr Chengkang Zhou and Professor Zi Yang Meng from the Department of Physics at The University of Hong Kong (HKU), and experimentalists Zhenyuan Zeng and Professor Shiliang Li at the Institute of Physics (IOP), Chinese Academy of Sciences (CAS), has led to a significant discovery in the field of quantum physics. Their research, published in Nature Physics, provides evidence for the existence of quasiparticles known as Dirac spinons within a novel quantum state called a quantum spin liquid state.
Quasiparticles are fascinating entities that emerge from collective behaviour within materials and can be treated as a group of particles. The Dirac spinons are expected to exhibit unique characteristics similar to Dirac particles in high-energy physics and the Dirac electrons in graphene and quantum moire materials, such as a linear dispersion relation between energy and momentum. However, these spin-½ charge neutral quasiparticles have not been observed in quantum magnets until this study.
The Hunt for Dirac Spinons in Quantum Magnets
The search for Dirac spinons in quantum magnets has been a long-standing goal for many condensed matter physicists. The discovery of these quasiparticles could potentially open up a myriad of applications for such highly entangled quantum material. “Who knows, maybe one day people will build quantum computers with it, just as people have been doing in the past half-century with silicon,” said Professor Meng, one of the corresponding authors of the paper.
The team’s investigation focused on a unique material known as YCu3-Br, characterised by a kagome lattice structure. Previous studies had suggested that this material could exhibit a quantum spin liquid state, making it an ideal candidate for exploration. The research team overcame numerous challenges to enable the observation of spinons in YCu3-Br, including assembling approximately 5000 single crystals together to meet the requirements for conducting experiments such as inelastic neutron scattering.
Observing Spinons in YCu3-Br
Using advanced techniques like inelastic neutron scattering, the team probed the material’s spin excitations and observed intriguing conical spin continuum patterns, reminiscent of the characteristic Dirac cone. While directly detecting single spinon proved challenging due to experimental limitations, the team compared their findings with theoretical predictions, revealing distinct spectral features indicative of the presence of spinons in the material.
The discovery provides compelling evidence for the existence of a Dirac quantum spin liquid state, which can be likened to a clear cry cutting through the fog of spectral investigation on the quantum spin liquid state. The findings not only advance our fundamental understanding of condensed matter physics but also open doors for further exploration into the properties and applications of YCu3-Br.
Quantum Spin Liquid State and Its Potential Applications
The quantum spin liquid state, characterised by the presence of fractional spinon excitations, is potentially relevant to high-temperature superconductivity and quantum information. In this state, the spins are highly entangled and remain disordered even at low temperatures. Therefore, investigating the spectral signals arising from spinons obeying the Dirac equation would provide a broader understanding of the quantum spin liquid state of matter. Such understanding also serves as a guidepost toward its broader applications, including the exploration of high-temperature superconductivity and quantum information.
The study was supported by the Ministry of Science and Technology of China, the Chinese Academy of Sciences and grants from Hong Kong Research Grants Council. The theoretical work of the paper was carried out by Dr Chengkang Zhou, a Postdoctoral Fellow at the Department of Physics, and his supervisor, Professor Zi Yang Meng. They are supported by the Collaborative Research Fund and ANR/RGC Joint Research Scheme of the Hong Kong Research Grants Council. The theoretical calculations conducted in this study were performed on the High-Performance Computing Platform at the Information Technology Services, HKU, and the ‘Blackbody’ supercomputer at the Department of Physics at HKU, as well as the Beijing PARATERA Tech CO., Ltd.
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