Search papers, labs, and topics across Lattice.
To resolve the lack of direct optical signatures for emergent altermagnetic phases, the authors characterized the insulating altermagnet La$_2$O$_3$Mn$_2$Se$_2$ using optical spectroscopy, inelastic neutron scattering, and first-principles calculations. They discovered mirror-image Stokes and anti-Stokes optical sidebands arising from pair emission and absorption between a spin-forbidden dark exciton and magnons, exactly matching the material's independently measured magnon density of states. Because the photoluminescence intensity quantitatively tracks the equal-time spin-spin correlator, this work proves that altermagnetic symmetry enables direct optical readout of coupled spin and dark-exciton dynamics.
Altermagnetic symmetry breaks the optical silence of spin-forbidden dark excitons, generating symmetric exciton-magnon sidebands that directly track underlying spin correlations.
Altermagnets'(AMs) non-relativistic spin splitting enables novel states, spintronic and magneto-optical devices, though their optical signatures remain elusive. Here, we report exciton-magnon emission and absorption: optical sidebands from a spin-forbidden dark exciton, a direct consequence of altermagnetic symmetry. Combined optical spectroscopy and first-principles calculations reveal that La$_2$O$_3$Mn$_2$Se$_2$ is an altermagnetic insulator, hosting a strongly bound, spin-forbidden dark exciton and a higher-energy bright exciton. Photoluminescence (PL) and absorption reveal mirror-image sidebands, Stokes-shifted in emission and anti-Stokes-shifted in absorption, symmetric about the dark exciton, whose energy shifts and spectral shapes match the magnon energy scale and density of states measured independently by inelastic neutron scattering. The PL intensity tracks the full equal-time spin-spin correlator, combining static and dynamical contributions, and rules out alternative processes. This directly couples PL to magnetism, with potential for magneto-optical devices. These results establish exciton-magnon spectroscopy as a new route for optically identifying and exploiting AMs.
