Abstract
Altermagnets uniquely exhibit non-relativistic spin polarization even in the absence of a net magnetization, thereby combining the advantages of ferromagnets and antiferromagnets and emerging as a promising platform for next-generation spintronic and quantum devices. However, the development of this emerging magnetism is fundamentally impeded by several critical ambiguities, including the lack of a physically transparent description in theory, smoking-gun verification in experiment, and extensive controversies in material realization. Therefore, this thesis systematically addresses these bottlenecks across three progressively structured dimensions. Firstly, we develop a unified symmetry decomposition framework based on C-paired spin-momentum locking (CSML), thus establishing a rigorous but physically transparent classification of altermagnets and uncovering the origins of various novel physical responses. Secondly, we provide a unified understanding of novel responses in altermagnets based on the CSML framework, thus identifying direct experimental fingerprints for altermagnet verification. Thirdly, after reviewing current controversies in representative altermagnetic candidates, we construct a realistic tight-binding model for the layered d-wave altermagnetic V2Se2O family, which enables an effective description of the low-energy physics of these novel materials and accounts for CSML-resulted phenomena, including noncollinear spin currents and the piezo-Hall effect. Together, these three complementary contributions provide a comprehensive outline for the understanding, application, and future exploration of altermagnetic materials.