Frozen State and Spin Liquid Physics in Na4Ir3O8: An NMR Study

Na4Ir3O8 is a unique case of a hyperkagome 3D corner sharing triangular lattice that 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 Na23 and O17 sites. We show that disordered magnetic freezing of all Ir sites sets in below Tf~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 induced by this exotic geometry. While the shift data show that the susceptibility levels off below 80 K, 1/T1 has little variation from 300 K to 2Tf. We discuss the implication of our results in the context of published experimental and theoretical work.