Detection of weak emergent broken-symmetries of the kagome antiferromagnet by Raman spectroscopy

We show that the magnetic Raman response of a spin liquid is independent of the polarizations of the light for triangular symmetries. In contrast, a ground state that has a broken-symmetry shows characteristic oscillations when the polarizations are rotated. This would allow one to detect weak broken-symmetries and emergent order parameters. We focus on the kagome antiferromagnet wherein no conventional long-range order has been found so far and present the Raman cross section of a spin liquid and a valence bond crystal by using a random phase approximation.

Figure 1

(Color online) Magnetic Raman cross section of the kagome lattice calculated within the RPA, which assumes a spin-liquid ground state. The response does not depend on the orientation of the incoming and outgoing photon polarizations ${\hat{\mathbf{e}}}_{\text{in}}$ or ${\hat{\mathbf{e}}}_{\text{out}}$. Each individual delta function is slightly broadened with a Lorentzian.

Figure 2

(Color online) Magnetic Raman cross section of the kagome lattice with weak broken-symmetry within the RPA. The ground state is supposed to be the valence bond crystal depicted in the inset that breaks the rotation symmetry (the correlations are assumed to be stronger on horizontal bonds). The different curves correspond to different orientations of the polarization vector ${\hat{\mathbf{e}}}_{\text{in}}\left(\parallel {\hat{\mathbf{e}}}_{\text{out}}\right)$.