Frozen State and Spin Liquid Physics in Na4Ir3O8: an NMR study

Na4Ir3O8 is a unique case of a hyperkagome 3D corner sharing triangular lattice which can be decorated with quantum spins. It has spurred a lot of theoretical interest as a spin liquid candidate. We present a comprehensive set of NMR data taken on both the 23Na and 17O sites. We show that disordered magnetic freezing of all Ir sites sets in below Tf $\sim$ 7 K, well below J = 300 K, with a drastic slowing down of fluctuations to a static state revealed by our T1 measurements. Above typically 2Tf, physical properties are relevant to the spin liquid state induce by this exotic geometry. While the shift data shows that the susceptibility levels off below 80 K, 1/T1 has little variation from 300K to 2Tf. We discuss the implication of our results in the context of published experimental and theoretical work.