Raman Circular Dichroism and Quantum Geometry of Chiral Quantum Spin Liquids

Abstract

We show that the quantum geometry of fractionalized spin excitations in Mott-insulating quantum spin liquids (QSL) gives rise to a finite Raman circular dichroism (RCD) signal. We demonstrate the equivalence between the Loudon-Fleury framework and the light-matter coupling approach for effective spinon bands. Using the latter, we derive an analytical decomposition of the RCD into different contributions of the quantum geometry. This reveals the sensitivity of the RCD to the underlying structure of the wave functions and the handedness of the excitations, rather than a nonzero Chern number of spinon excitations. To illustrate this, we apply our approach to two examples, the Kitaev honeycomb model in a magnetic field and a chiral $U(1)$ QSL on the triangular lattice, and discuss its experimental relevance for candidate materials.