Linear and nonlinear optical investigations of altermagnet semiconductor La₂O₃Mn₂Se₂

Altermagnetism, a novel class of magnetic phase where two opposite magnetic sublattices are connected by time reversal combined with rotation, exhibits nonrelativistic spin band splitting while maintaining zero net magnetization.. Such magnetic phase is reported to be realized in La₂O₃Mn₂Se₂ (LOMSe), a tetragonal oxychalcogenide containing a two-dimensional Mn₂O layer that forms an inverse Lieb lattice. The presence of the inverse Lieb lattice allows LOMSe to be a d-wave type altermagnet, one of the simplest realizations of the altermagnetic order, making it an ideal platform for studying altermagnetism. LOMSe is reported to be a Mott insulator with strong correlation, which, in combination with the inverse Lieb lattice structure, indicates it host high density of state. Combining with density functional theory (DFT) calculations showing LOMSe to have a large bandgap (>1.5 eV), LOMSe is thereby an excellent platform for investigation magneto-optical properties out of altermagnetism. Hence, we perform linear and nonlinear optical experiments on LOMSe to study whether and how they evolve across the altermagnetic phase transition. In this talk, I will present our results of linear and circular dichroism in LOMSe for the detection of piezomagnetism, a key signature of d-wave altermagnetism, and second and third harmonic generation for the resolution of altermagnetic domain states, a natural consequence of C₄T symmetry in the altermagnetic phase.