  Taken together, time-reversal and spatial inversion symmetries impose a
two-fold spin degeneracy of the electronic states in crystals. In
centrosymmetric materials, this degeneracy can be lifted by introducing
magnetism, either via an externally applied field or through internal
magnetization. However, a correlated alignment of spins, even in the
paramagnetic phase, can lift the spin degeneracy of electronic states. Here, we
report an in-depth study of the electronic band structure of the Eu-ternary
pnictide EuZn2Sb2 through a combination of high-resolution angle-resolved
photoemission spectroscopy measurements and first principles calculations. An
analysis of the photoemission lineshapes over a range of incident photon
energies and sample temperatures is shown to reveal the presence of band spin
degeneracy-lifting in the paramagnetic phase. Our ARPES results are in good
agreement with theoretical ferromagnetic-phase calculations, which indicates
the importance of ferromagnetic fluctuations in the system. Through our
calculations, we predict that spin-polarized bands in EuZn2Sb2 generate a
single pair of Weyl nodes. Our observation of band-splitting in EuZn2Sb2
provides a key step toward realizing time-reversal symmetry breaking physics in
the absence of long-range magnetic order.
