In the realm of materials science, understanding the properties of matter in different states is crucial for technological advancements. Liquid crystal, for instance, is a remarkable state of matter that exhibits characteristics of both liquids and solids. However, its magnetic counterpart, known as the “spin-nematic phase,” had remained elusive for over half a century. This enigmatic phase is characterized by spin moments taking on the role of the constituent molecules. While conventional experimental techniques were unable to observe the spin quadrupoles, which are the defining features of this phase, a team led by Professor Kim Bumjoon at the IBS Center for Artificial Low-Dimensional Electronic Systems in South Korea has managed to make a groundbreaking discovery. Through their remarkable achievements in synchrotron facility development, they directly observed spin quadrupoles for the first time in history.
To uncover the secrets of the spin-nematic phase, the researchers at the IBS Center focused their study on a material called square-lattice iridium oxide Sr2IrO4. This particular material had previously been acknowledged for its antiferromagnetic dipolar order at low temperatures. In their research, they were able to unveil the coexistence of a spin quadrupolar order by observing its interference with the magnetic order. The detection of this interference signal was made possible through the novel technique of circular-dichroic resonant X-ray diffraction, which utilizes a circularly polarized X-ray beam. These findings were further verified using polarization-resolved resonant inelastic X-ray scattering, which revealed magnetic excitations that deviated significantly from those expected in conventional magnets.
To complete these groundbreaking experiments, the researchers collaborated with the Argonne National Laboratory in the United States to establish a resonant inelastic X-ray scattering beamline at the Pohang Accelerator Laboratory in South Korea. The construction of this beamline spanned over four years and represented a significant investment of time and effort. Through the use of optical techniques such as Raman spectroscopy and magneto-optical Kerr effect measurement, the researchers demonstrated that the formation of spin quadrupole moments occurs at higher temperatures than magnetic order. This observation implies the existence of a spin-nematic phase in the material, where only spin quadrupole moments are present.
The successful observation of the spin quadrupoles in the spin-nematic phase has tremendous implications for various fields of science and technology. Professor Kim Bumjoon, corresponding author of the study, emphasized that this research became possible due to the globally competitive level of X-ray experimental infrastructure and capabilities in South Korea. Additionally, Professor Cho Gil Young, a co-author of the study and a professor at Pohang University of Science and Technology, highlights the significance of this discovery for quantum computing and information technologies. The highly entangled spins in the spin-nematic phase, as suggested by physicist P. W. Anderson, may serve as a critical ingredient for achieving high-temperature superconductivity.
One of the most fascinating aspects of the spin-nematic phase is its potential relationship with high-temperature superconductivity. The entanglement of spins in this phase resembles a critical requirement proposed by physicist P. W. Anderson for achieving high-temperature superconductivity. The similarity between iridium oxide Sr2IrO4 and the copper-oxide high-temperature superconducting system has sparked growing interest in this material as a potential platform for new high-temperature superconducting systems. By delving deeper into the intricate properties of the spin-nematic phase, researchers may uncover new insights into the mechanisms behind high-temperature superconductivity.
The direct observation of spin quadrupoles in the spin-nematic phase represents a groundbreaking achievement in the field of materials science. Through innovative experimental techniques and collaborative efforts, the team led by Professor Kim Bumjoon has uncovered the hidden properties of the square-lattice iridium oxide Sr2IrO4. This discovery not only provides insights into the spin-nematic phase but also holds significant implications for quantum computing, information technologies, and the quest for high-temperature superconductivity. Moving forward, further exploration of this phase may unveil new opportunities for advancing our understanding of complex materials and their applications in various fields.
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