Optical Observation of Quasiperiodic Heisenberg Antiferromagnets in Two Dimensions

A spin‐wave analysis of magnetic Raman scattering in an antiferromagnetic Heisenberg model on the 2D Penrose lattice of C5v point symmetry is made. Following the Shastry–Shraiman perturbation scheme for a strongly correlated Hubbard model, fourth‐order effective Raman operators are obtained. Within the second‐order mechanism, there is one and only Raman active mode of E2 symmetry, yielding a spectral weight independent of light polarization. Considering the fourth‐order scatterings as well, activates A1 and A2 as well as E2 modes and therefore results in polarization‐dependent Raman spectra. With the use of linearly and circularly polarized lights, all the symmetry species can separately be extracted from observations. Though the linear spin‐wave theory, i.e., the harmonic oscillator approximation, is far from quantitative, the A2 and E2 Raman intensities are well describable with two magnon interactions. The Raman‐active A1 mode owes much to higher‐order magnon–magnon interactions as well. Theoretical calculations of the magnetic Raman scattering on the 2D quasiperiodic Heisenberg antiferromagnets are reported. The Raman scattering intensity profile detects various magnetic excitations, including spin‐chirality fluctuations. The interactions between magnons play an important role in the magnetic Raman scattering process.