Observation of a giant band splitting in altermagnetic MnTe

We performed angle-resolved photoemission spectroscopy (ARPES) on hexagonal MnTe, a candidate for an altermagnet with a high critical temperature (TN=307K). By utilizing photon-energy-tunable ARPES in combination with first-principles calculations, we found that the band structure in the antiferromagnetic phase exhibits a strongly anisotropic band-splitting associated with the time-reversal-symmetry breaking, providing direct experimental evidence for the altermagnetic band splitting. The magnitude of the splitting reaches 0.8 eV at non-high-symmetry momentum points, which is much larger than the spin-orbit gap of ∼0.3 eV along the ΓK high-symmetry cut. The present result paves the way toward realizing exotic physical properties associated with the altermagnetic spin splitting.