Effects of Na deficiency on spin dynamics in the Mott insulating Na4-xIr3 O8

We report on Raman scattering and Na23 nuclear magnetic resonance (NMR) investigations of jeff=1/2 hyperkagome antiferromagnet Na4-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 Na4-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 Na23 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.