Twisted CrPS4 Layers Show Altermagnetism
Researchers have experimentally demonstrated altermagnetism, a distinct magnetic state, in a homostructure created by twisting two layers of the van der Waals material CrPS4.
Scientists have reported the first direct experimental observation of altermagnetism in a twisted van der Waals material. The discovery was made in a homostructure built from two layers of chromium thiophosphate (CrPS4) rotated 90 degrees relative to each other. Altermagnetism bridges the gap between ferromagnetism and antiferromagnetism. It is characterized by a compensated, antiparallel spin order that nonetheless produces a finite spin splitting in electronic bands. This property makes it promising for next-generation spintronic applications. Direct proof in engineered van der Waals systems had been elusive.
Evidence from Magneto-Optical Spectroscopy
The research team, reporting in Nature Physics, used magneto-Optical spectroscopy to probe the twisted CrPS4/CrPS4 structure. They observed a magnetic-field dependence in the degree of circular polarization. This resembled the behavior of a ferromagnet. Crucially, a pronounced Zeeman splitting emerged in the twisted configuration. This splitting is absent in both the standard ferromagnetic and antiferromagnetic phases of CrPS4. It signals a distinct magnetic ground state.
Computational Confirmation of Spin Splitting
First-principles calculations performed by the group provided the theoretical underpinning for the experimental signals. The calculations revealed the presence of large spin-split bands. The material maintained an antiferromagnetic configuration. This combination is the definitive hallmark of an altermagnetic state. The work confirms that twisting van der Waals layers can induce altermagnetism by tuning interlayer symmetry. Previous theoretical studies had suggested this.
Unique Phonon Signature from Raman Spectroscopy
Further evidence came from polarized Raman spectroscopy. The technique identified a splitting of specific phonon modes. This splitting was induced by the interlayer coupling in the twisted configuration. The phonon-mode splitting is unique to the altermagnetic state. It provides an additional experimental fingerprint beyond the electronic structure measurements.
Implications for Magnetic Material Design
The findings demonstrate that the 'twistronics' approach is a viable method for creating and controlling altermagnetic states. This expands the family of available magnetic quantum materials. The study's authors state their work provides experimental evidence of altermagnetism in a twisted van der Waals material. By moving from theoretical suggestion to physical observation, the research opens a path for designing new materials with tailored spin properties for advanced electronics. The data supporting the findings are available within the Article and its Supplementary Information. Extra data are available from the corresponding author on request.
