Spectra of a gapped quantum spin liquid with a strong chiral excitation on the triangular lattice

Abstract

While a quantum spin liquid (QSL) phase has been identified in the $J_1$-$J_2$ Heisenberg model on a triangular lattice via numerical calculations, debate persists about whether or not such a QSL is gapped or gapless, with contradictory conclusions from different techniques. Moreover, information about excitations and dynamics is crucial for the experimental detection of such a phase. In this work, we use exact diagonalization to characterize signatures of a QSL phase on the triangular lattice through the dynamical spin structure factor $\mathcal{S}(q,\omega)$ and Raman susceptibility $\mathcal{\chi}(\omega)$. We find that spectra for the QSL phase show distinct features compared to those of neighboring phases; and both the Raman spectra and spin structure factor show gapped behaviour in the QSL phase. Interestingly, there is a prominent excitation mode in the Raman $A_2$ channel, indicating a strong subleading tendency toward a chiral spin liquid phase.