Effects of Na deficiency on spin dynamics in the Mott insulating Na4−xIr3O8

We report on Raman scattering and ²³Na nuclear magnetic resonance (NMR) investigations of jeff=1/2 hyperkagome antiferromagnet Na_4-xIr₃O₈, which lies in the Mott insulating state. Our Raman scattering experiments unveil remarkable parallels between the magnetic excitations of the pristine Na₄Ir₃O₈ and the Kitaev honeycomb material Na₂IrO₃, which are characterized by dominant fractional spinon excitations. In the case of moderate Na-deficient Na_4-xIr₃O₈, however, a substantial suppression of the magnetic excitations is observed, alluding to the notable influence of charge fluctuations on spin dynamics. In addition, our site-specific ²³Na NMR measurements offer further insights into the spin dynamics when a minor concentration of holes is introduced into a spin-orbit coupled Mott insulator. Specifically, the spin-lattice relaxation rate 1/T₁ reveals the emergence of pseudogaplike correlations at the Na(2) site, alongside a critical slowing down behavior at the Na(1) and Na(3) sites. These findings showcase the intricate interplay between itinerant holes and magnetic correlations in a spin-liquid-like background.