Altermagnetic Lifting of Kramers Spin Degeneracy

Researchers have discovered a new magnetic phase called altermagnetism that can lift the Kramers spin degeneracy in materials. This phase allows for the separation of spin degeneracy without net magnetization and inversion symmetry breaking.



The existence of a lifted Kramers spin degeneracy (LKSD) has long been a topic of interest in condensed-matter physics. LKSD is responsible for various practical applications and ongoing research in areas like magnetic-memory technology and topological quantum matter. Until now, it was believed that LKSD could only arise from two internal symmetry-breaking mechanisms: time-reversal symmetry breaking by magnetization of ferromagnets and inversion symmetry breaking in crystals. However, a recent study has identified a new magnetic phase, called altermagnetism, that allows for the lifting of spin degeneracy without net magnetization and inversion-symmetry breaking.

Unconventional Magnetic Phase

In this study, the researchers confirmed the existence of altermagnetic LKSD using photoemission spectroscopy and ab initio calculations. They focused on a centrosymmetric MnTe material and found two distinct mechanisms of LKSD generated by the altermagnetic phase. The researchers suggest that the observation of altermagnetic LKSD could have significant implications for the field of magnetism, as it motivates further exploration and exploitation of this unconventional magnetic phase.

Consequences and Applications

The discovery of altermagnetic LKSD has the potential to enrich various fields, including spintronics, ultrafast magnetism, magnetoelectrics, and topological matter. The researchers propose that the strong altermagnetic LKSD mechanism could enable spin-polarized currents similar to those used in ferromagnetic memory devices but without the limitations imposed by net magnetization. On the other hand, the weak altermagnetic LKSD mechanism has been linked to dissipationless anomalous Hall currents and shows potential for realizing robust quantum-topological effects.

Experimental confirmation of altermagnetic LKSD has already been achieved in materials like RuO2 and MnTe, where several expected macroscopic time-reversal-symmetry-breaking responses have been observed. The researchers propose further investigations into the unconventional nature of altermagnets and their potential applications in various materials, including insulators, semiconductors, metals, and superconductors.