Spin liquid like Raman signatures in the hyperkagome iridate Na4Ir3O8

Combining Raman scattering measurements with mean-field calculations of the Raman response, we show that Kitaev-like magnetic exchange is dominant in the hyperkagome iridate ${\mathrm{Na}}_{4}{\mathrm{Ir}}_{3}{\mathrm{O}}_{8}$. In the measurements we observe a broad Raman band at $\ensuremath{\sim}3500\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ with a bandwidth $\ensuremath{\sim}1700\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Calculations of the Raman response of the Kitaev-Heisenberg model on the hyperkagome lattice shows that the experimental observations are consistent with the calculated Raman response where the Kitaev exchange interaction (${J}_{K}$) is much larger than the Heisenberg term ${\mathrm{J}}_{1}$ (${J}_{1}/{J}_{K}\ensuremath{\sim}0.1$). A comparison with the theoretical model gives an estimate of the Kitaev exchange interaction parameter.