Abstract:
The third class of magnetism, dubbed as altermagnetism, has been a recent hot topic in the field of magnetism. Some of the collinear antiferromagnets have spin-split bands contrary to the conventional wisdom. These altermagnets therefore have characteristics of both ferro- (FM) and antiferro-magnetism (AFM): spin split bands (thus broken time reversal symmetry) and zero net magnetization. These traits are believed to be important in the fundamental scientific point of view as well as for spintronic applications.In this colloquium talk, I first wish to introduce the concept of altermagnetism. I will first talk about ABCs of altermagnetism – collinear AFM (zero net magnetization) and spin split bands (time reversal symmetry breaking) in terms of symmetries. Then, I will discuss the microscopic origin of the spin splitting based on the AFM order and structural distortion. This shows how spin and orbital are entangled, eventually leading to the multipole order, that is, the order parameter of altermagnets.Experimental verification of altermagetism is inherently difficult due to the zero net magnetization as well as domain formation. Yet, evidences for spin split bands can be obtained in some cases. I will introduce our recent ARPES work on an altermagnet MnTe. ARPES data show split bands which merges to a single band above the Neel temperature, strongly indicating the magnetic origin of the splitting. Finally, I will also briefly introduce recent study results on magnetic responses of RuO2 and domain switching behavior in MnTe/Bi2Te3 hetero structures.