Effects of Na deficiency on spin dynamics in the Mott insulating Na 4- x Ir 3 O 8

We report on Raman scattering and 23 Na nuclear magnetic resonance (NMR) investigations of j eff = 1 / 2 hyperkagome antiferromagnet Na 4- x Ir 3 O 8 , which lies in the Mott insulating state. Our Raman scattering experiments unveil remarkable parallels between the magnetic excitations of the pristine Na 4 Ir 3 O 8 and the Kitaev honeycomb material Na 2 IrO 3 , which are characterized by dominant fractional spinon excitations. In the case of moderate Na-deficient Na 4- x Ir 3 O 8 , 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 23 Na 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 / T 1 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.