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Research Background
Research Background
Kondo lattice systems, one of the central subjects in modern condensed matter physics, are characterized by correlations between conduction electrons and localized spins. These interactions give rise to a variety of remarkable quantum phenomena, including heavy-fermion behavior, quantum criticality, and unconventional superconductivity. The Kondo necklace model, proposed by Sebastian Doniach in 1977, is a simplified quantum-spin model that captures the essential spin degrees of freedom of a one-dimensional Kondo lattice. Theoretical studies have predicted a rich variety of ground states depending on the magnitude of the decorated spins and the strength of the Kondo coupling. Furthermore, external magnetic fields can induce quantum phase transitions and stabilize novel quantum states. Despite its importance as a fundamental model for strongly correlated quantum matter, an experimental realization of the Kondo necklace model had remained an outstanding challenge for decades.
Kondo lattice systems, one of the central subjects in modern condensed matter physics, are characterized by correlations between conduction electrons and localized spins. These interactions give rise to a variety of remarkable quantum phenomena, including heavy-fermion behavior, quantum criticality, and unconventional superconductivity. The Kondo necklace model, proposed by Sebastian Doniach in 1977, is a simplified quantum-spin model that captures the essential spin degrees of freedom of a one-dimensional Kondo lattice. Theoretical studies have predicted a rich variety of ground states depending on the magnitude of the decorated spins and the strength of the Kondo coupling. Furthermore, external magnetic fields can induce quantum phase transitions and stabilize novel quantum states. Despite its importance as a fundamental model for strongly correlated quantum matter, an experimental realization of the Kondo necklace model had remained an outstanding challenge for decades.
Using our proprietary RaX-D (Radical-based crystal eXpansion-Design) strategy, which enables precise control of the spatial arrangement and interactions of organic radical spins, we achieved the world's first experimental realization of the Kondo necklace model, a quantum-spin model that had long remained a theoretical concept.
In a molecular quantum magnet composed of organic radicals and cobalt ions, we demonstrated the formation of a necklace-like spin structure characteristic of the Kondo necklace model. Furthermore, we discovered a magnetic-field-induced switching of spin-coupling states, whereby the quantum-entangled spin network can be selectively modified by an external magnetic field. This finding highlights the potential of molecular quantum materials for future applications in quantum information technologies and spintronics.
Highlights
Highlights
First experimental realization of a Kondo necklace model in a hybrid magnetic material composed of organic radicals and cobalt ions.
Observation of quantum-entangled states in a designed spin system.
Demonstration of magnetic-field control of spin-coupling states, providing a foundation for novel functional quantum materials.
2. New quantum boundary discovered: Spin size determines how the Kondo effect behaves
2. New quantum boundary discovered: Spin size determines how the Kondo effect behaves
Commun. Mater. 7, 5 (2026) Press release
Phys.org — “New quantum boundary discovered: Spin size determines how the Kondo effect behaves”
ScienceDaily — “A tiny spin change just flipped a famous quantum effect”
Laser Focus World — “Quantum switch?”
Innovation News Network — “Quantum rule-break: Spin size rewrites the Kondo effect”
AZoQuantum — “Precise Control of Magnetic Interactions via RaX-D”
Enerzine.com — “Des chercheurs japonais trouvent une énigme de physique quantique vieille de près de 50 ans”
日刊工業新聞—"大阪公立大など、スピンで量子状態制御 大きさに着目"
Building upon our previous realization of the Kondo necklace model, we demonstrated for the first time, through a combination of experiment and theory, that the nature of the Kondo effect changes fundamentally with the size of the decorated spins. In particular, we discovered that the Kondo effect—traditionally known for suppressing magnetic order—can instead promote the emergence of magnetism in systems with spin-1 moments.
Using a hybrid molecular quantum magnet composed of organic radicals and nickel ions, we designed and realized a new type of Kondo necklace system. Experimental observations, supported by theoretical analyses, revealed a qualitative change in the role of the Kondo coupling as the spin size increases. This finding establishes a new boundary in quantum many-body physics and introduces spin size as a powerful new parameter for engineering quantum phases.
Highlights
Highlights
Designed and realized a new Kondo necklace system in a hybrid magnetic material composed of organic radicals and nickel ions.
Demonstrated that the role of the Kondo effect can switch from suppressing magnetism to generating magnetic order depending on the spin size.
Introduced spin size as a new design parameter for controlling quantum phases and emergent quantum states.
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