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Researchers have developed the first direct optical method to measure interlayer spin correlations in layered magnetic materials using two-magnon Raman scattering. Testing this technique on the van der Waals antiferromagnet CrSBr, they found the signal matched theoretical predictions without requiring parameter fitting and disappeared when the material transitioned to a ferromagnetic state under an applied magnetic field. The team also demonstrated an exciton-mediated enhancement that amplified the signal approximately tenfold when the laser frequency was tuned near the exciton resonance.
Why it matters
This technique provides experimentalists with a new tool to probe fundamental magnetic properties in two-dimensional materials that were previously inaccessible to direct measurement. The method could be applied to study exotic quantum phenomena in twisted magnetic bilayers and heterostructures, potentially advancing the development of spintronic devices and quantum materials.
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⚠️ Preprint – Noch nicht peer-reviewed
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Abstract: Spin correlations govern numerous collective behaviors of quantum materials, underpinning exotic phenomena such as unconventional superconductivity and topological magnetism. In layered materials, the interlayer spin correlation is important because it characterizes the magnetic ground state and determines spin transport across the interface. Yet interlayer spin correlations have remained hard to measure directly, leaving one of the most basic quantities of two-dimensional magnetism out of experimental reach. Here we provide the first direct optical probe of interlayer spin correlations, using two-magnon Raman scattering in the van der Waals antiferromagnet (AFM) CrSBr, in remarkable agreement with a microscopic spin-wave model without any fitting parameter. Moreover, the two-magnon channel switches on only in the AFM state and vanishes when a magnetic field takes the crystal to a ferromagnetic state. We furthermore establish an exciton-mediated variant of the technique, where tuning the laser near the exciton resonance enhances the signal roughly tenfold due to the exciton’s large oscillator strength. Magnon-pair Raman spectroscopy thus opens a direct optical window into interlayer spin correlations in van der Waals magnets, extendable to twisted bilayers and proximity-coupled heterostructures.