  Altermagnetism represents an emergent collinear magnetic phase with
compensated order and an unconventional alternating even-parity wave spin order
in the non-relativistic band structure. We investigate directly this
unconventional band splitting near the Fermi energy through spinintegrated soft
X-ray angular resolved photoemission spectroscopy. The experimentally obtained
angle-dependent photoemission intensity, acquired from epitaxial thin films of
the predicted altermagnet CrSb, demonstrates robust agreement with the
corresponding band structure calculations. In particular, we observe the
distinctive splitting of an electronic band on a low-symmetry path in the
Brilliouin zone that connects two points featuring symmetry-induced degeneracy.
The measured large magnitude of the spin splitting of approximately 0.6 eV and
the position of the band just below the Fermi energy underscores the
signifcance of altermagnets for spintronics based on robust broken time
reversal symmetry responses arising from exchange energy scales, akin to
ferromagnets, while remaining insensitive to external magnetic fields and
possessing THz dynamics, akin to antiferromagnets.
