Photoluminescence as a table top probe of Altermagnetism in the Lieb-Lattice La₂O₃Mn₂Se₂

Altermagnetism opens a new route to correlated states that couple lattice and spin symmetries, but direct tabletop probes of the Altermagnetic (AM) state remain elusive. Here, I will discuss our efforts to fill this gap by exploring the optical response of La₂O₃Mn₂Se₂. This compound was recently reported to host a Mott-insulating AM state on the Lieb lattice, though direct evidence of such a state is elusive. First, I will discuss the optical absorption and photoluminescence (PL) measurements, which combined with the first-principles calculations demonstrate that La₂O₃Mn₂Se₂ is a charge-transfer insulator with a strong on-site Hubbard interaction. Furthermore, temperature, excitation energy, and power dependent PL measurements, together with neutron scattering, prove it is magnon-mediated emission from a spin-forbidden (dark) state, both direct consequences of the Altermagnetism.