Magnetic correlations in the semimetallic hyperkagome iridate Na₃Ir₃O₈: a rare case of doping in a quantum spin liquid

A decade ago the first realization of an effective spin 1/2 hyper-kagome lattice was discovered in the form of Na₄Ir₃O₈, which is an insulator and was found to exhibit spin freezing at ~7 K .

Na₃Ir₃O₈ has a different crystal structure, but the underlying hyperkagome arrangement of iridium ions is preserved. Moreover, the iridium valence in this system is 4.33+ and not 4+ like in the parent compound. Therefore, it can be seen as a 1/3 hole doped hyper-kagome spin system, a rare example of efficient doping achieved in a quantum spin liquid, following P.W. Anderson's seminal idea. Due to a complex interplay between inter-site hopping, Coulomb repulsion, crystal field splitting and spin-orbit coupling, it is a semi-metal.

We present a microscopic ²³Na NMR study of the Na₃Ir₃O₈ compound. The uniform q = 0 susceptibility is determined via shift measurements and the dynamical response by probing the spin-lattice relaxation rate. The susceptibility is consistent with a semimetal behavior, though with electronic bands substantially modified by correlations. Remarkably, the antiferromagnetic fluctuations present in the insulating parent compound Na₄Ir₃O₈ survive in the studied compound. The spin dynamics are consistent with 120° excitations modes displaying short-range correlations.