  Recently, a new kind of collinear magnetism, dubbed altermagnetism, has
attracted considerable interests. A key characteristic of altermagnet is the
momentum-dependent band and spin splitting without net magnetization. However,
finding altermagnetic materials with large splitting near the Fermi level,
which necessarily requires three-dimensional k-space mapping and is crucial for
spintronic applications and emergent phenomena, remains challenging. Here by
employing synchrotron-based angle-resolved photoemission spectroscopy (ARPES)
and model calculations, we uncover a large altermagnetic splitting, up to ~1.0
eV, near the Fermi level in CrSb. We verify its bulk-type g-wave altermagnetism
through systematic three-dimensional kspace mapping, which unambiguously
reveals the altermagnetic symmetry and associated nodal planes. The ARPES
results are well captured by density functional theory calculations. In
addition, tight-binding model analysis indicate that the large altermagnetic
splitting arises from strong third-nearest-neighbor hopping mediated by Sb
ions, which breaks both the space-time reversal symmetry and the translational
spin-rotation symmetry. The large band/spin splitting near Fermi level in
metallic CrSb, together with its high TN (up to 705 K) and simple spin
configuration, paves the way for exploring emergent phenomena and spintronic
applications based on altermagnets.
