Absence of spin splitting in altermagnetic CrSb epitaxial thin films

Altermagnets, a novel quantum state of matter, exhibit unique momentum-dependent spin-split band structures even in the absence of spin-orbit coupling (SOC), driven by crystal rotation or mirror symmetry operations. However, nanoscale altermagnets display markedly different physical properties from their bulk counterparts due to quantum confinement and dimensional reduction effects. Addressing a gap in direct spectroscopic studies, we present the first visualization of the electronic structure in CrSb epitaxial thin films, advancing understanding of this recently identified altermagnetic material. Utilizing spin-resolved angle-resolved photoemission spectroscopy (spin-ARPES) and first-principles calculations, we identified distinct signatures of 3D g-wave altermagnetism in CrSb via systematic k-space mapping. Despite the clear band dispersion, CrSb thin films exhibited no net spin signals along both low-symmetry and high-symmetry paths in the Brillouin zone, a surprising finding that challenges existing theories. This study not only deepens our understanding of the unique properties of CrSb films but also sets the stage for future explorations into their exotic behaviors and practical applications, highlighting the critical interplay between crystal rotational symmetry, magnetic order, and electronic band structure.