In the rapidly evolving field of magnetism, altermagnets stand out for their remarkable ability to exhibit spin-splitting bands within antiferromagnetic frameworks, all while maintaining crystal-symmetry-paired spin-momentum locking (CSML) without spin-orbit coupling. This unique blend unlocks intriguing phenomena, including unconventional piezomagnetism and noncollinear spin currents, holding immense promise for advanced spintronics applications. Despite growing excitement, achieving a true atomically thin or two-dimensional monolayer altermagnet in experiments has proven challenging, many prior theoretical efforts lack solid experimental backing, the closest successes to date are layered compounds like K- or Rb-intercalated V2(Se,Te)2O, recently verified by two independent works in Nature Physics [https://doi.org/10.1038/s41567-025-02864-2; https://doi.org/10.1038/s41567-025-02822-y], directly following theoretical predictions in Nature Communications in 2021 [https://doi.org/10.1038/s41467-021-23127-7] by a research team led by Prof. Junwei Liu from Department of Physics at the Hong Kong University of Science and Technology (HKUST).
To overcome this gap, the same team led by Prof. Junwei Liu has introduced a symmetry-guided design strategy by using V2(Se,Te)2O as template in their latest published results in National Science Review, an up-do-date advance of their previous prediction and validation of 2D altermagnetism. Drawing directly from the symmetry of its atomic structure and magnetic sublattices, their design strategy emphasizes symmetry-preserving tweaks of atomic sites and valence-adaptive substitution of chemical elements. These proposals prioritize the realization of altermagnetic order at ground state, as well as the higher feasibility in synthesis and stability.
This team systematically designed four core structural prototypes: M2A2B and M2A2 (with M as transition metals and A/B from pnictogens, chalcogens, or halogens) together with their asymmetric Janus variants M2AA'B and M2AA'. By enforcing rules like robust covalent bonding, closed-shell stability, and balanced valences, they assembled a large library of 2600 candidate compounds. High-throughput first-principles calculations scrutinized these candidates for ground-state magnetic orders (altermagnetic, antiferromagnetic, ferromagnetic, and non-magnetic) and electronic structures (semiconducting, metallic, half-metallic, and Dirac-cone), pinpointing 612 potential altermagnets featuring CSML, a success rate approaching 1/4 highlighting the precision of their strategy.
A standout 79 altermagnets simultaneously combines CSML to Dirac-cone energy bands—linear gapless band crossings near the Fermi level—to facilitate massless carriers for spin-selective ultrafast transport. This dual property sets the stage for ultrafast, anisotropic, and crystal symmetry tunable spin currents in nanostructures, more advantageous than conventional magnetic materials in the field of spintronics. Their findings reveal element-dependent trends: altermagnetic order thrives with specific transition metals and avoids different "absent belts" in each structural prototypes, while it shows pronounced preference on non-metal elements in M2A2B and Janus variant M2AA'B but becomes insensitive in M2A2 and M2AA'. The wide-spanning spectrum of electronic behaviors, from semiconducting and metallic to half-metallic and Dirac semi-metallic, not only uncovers how chemical substitution and Stark effect from Janus structuring tweak electronic states and hybridization but also offers versatility for applications of different purposes. Stability checks via phonon calculations and molecular dynamics simulations confirm the highly feasibility of many representative altermagnets predicted in synthesis.
What sets this HKUST-led effort apart from typical computational screenings is its dual focus: not just forecasting a trove of potentially synthesizable monolayer altermagnets but forging a rational and universal design playbook that can extend to other systems, including 3D bulks. By bridging theory with experimental roots, it accelerates progress toward material synthesis and understanding of physics and property tuning. Prof. Liu's team envisions this work as a springboard for future experimental synthesis and in-depth probes into altermagnetic physics and phenomena.
*Corresponding authors of the article are Prof. Junwei Liu and Dr. Runzhang Xu from HKUST. The theoretical works and high-throughput calculations were conducted by HKSUT Postdoctoral researcher Runzhang Xu and PhD student Yifan Gao. This work is available online as https://doi.org/10.1093/nsr/nwaf528 .
