Optical observation of quasiperiodic Heisenberg antiferromagnets in two dimensions

We calculate magnetic Raman spectra of Heisenberg antiferromagnets on the two-dimensional Penrose lattice. We follow the Shastry-Shraiman formulation of Raman scattering in a strongly correlated Hubbard system and obtain the second- and fourth-order effective Raman operators. The second-order Raman intensity comes from the E2 mode, and it is invariant under an arbitrary rotation of polarization vectors. The fourth-order Raman intensities consist of A1 and A2, as well as E2, modes and therefore yield strong polarization dependence. In particular, the A2 mode intensity directly detects the dynamical spin-chirality fluctuations. Employing linearly and circularly polarized lights, we can separately extract every irreducible representation from the observations. We further discuss effects of magnon-magnon interactions on the magnetic Raman scattering. Our theory provides a reasonable explanation for the two-magnon scattering process.