Signature of antiferromagnetic long-range order in the optical spectrum of strongly correlated electron systems

We show how the onset of a non-Slater antiferromagnetic ordering in a correlated material can be detected by optical spectroscopy. Using dynamical mean-field theory we identify two distinctive features: The antiferromagnetic ordering is associated with an enhanced spectral weight above the optical gap, and well-separated spin-polaron peaks emerge in the optical spectrum. Both features are indeed observed in LaSrMnO4 [A. Gossling et al., Phys. Rev. B 77, 035109 (2008)].