Spin size rewrites the Kondo effect
Quantum effects in Kondo lattices decide whether a material behaves magnetically or not. This opens new opportunities for designing future quantum materials and technologies.
The Kondo effect, where localized spins interact with conduction electrons, underpins many quantum phenomena. But in real materials, extra factors like charge and orbital motion make it hard to isolate the effect of spin alone.
The Kondo necklace model
The Kondo necklace model, proposed in 1977 by Sebastian Doniach, simplifies the problem by focusing only on spins. It has long been a key tool for exploring new quantum states. However, realizing it experimentally has been challenging for decades.
A key question is whether the Kondo effect depends on the size of the local spin. Understanding this would be important for quantum material research worldwide.
Realizing spin-dependent Kondo behavior
Researchers led by Associate Professor Hironori Yamaguchi at Osaka Metropolitan University created a Kondo necklace using an organic-inorganic hybrid of organic radicals and nickel ions.
Using the RaX-D molecular design framework, they precisely controlled the crystal arrangement and magnetic interactions. This allowed them to compare spin-1/2 and spin-1 Kondo necklaces in a clean, spin-only system.
Thermodynamic measurements showed a clear phase transition: increasing the spin from 1/2 to 1 changed the system from nonmagnetic to a long-range magnetic order. Quantum analysis confirmed that Kondo coupling mediates effective magnetic interactions between spin-1 moments.
Overturning traditional theory
Traditionally, the Kondo effect was thought to suppress magnetism by forming singlets with zero total spin. This study shows that when the spin exceeds 1/2, the same interaction actually promotes magnetic order.
This experiment provides the first direct evidence that the Kondo effect behaves differently depending on spin size. Spin-1/2 forms local singlets, while spin-1 and higher stabilize magnetic order.
Implications for quantum materials
This discovery offers a new perspective on quantum matter. Controlling spin size allows researchers to switch quantum states between nonmagnetic and magnetic regimes.
Professor Yamaguchi explained that this principle provides a powerful design strategy for next-generation quantum materials. It could guide the creation of spin-based quantum devices, including components for quantum information and computing.
Next steps
Understanding how to control whether a Kondo lattice becomes magnetic or nonmagnetic is vital for future quantum technologies. It affects entanglement, magnetic noise, and quantum criticality.
The team hopes these insights will inspire new quantum materials and advance emerging quantum technologies.
