Exotic Low-Energy Excitations Emergent in the Random Kitaev Magnet Cu2IrO3

We report on magnetization M(H), dc and ac magnetic susceptibility chi(T), specific heat C-m(T) and muon spin relaxation (mu SR) measurements of the Kitaev honeycomb iridate Cu2IrO3 with quenched disorder. In spite of the chemical disorders, we find no indication of spin glass down to 260 mK from the C-m(T) and mu SR data. Furthermore, a persistent spin dynamics observed by the zero-field muon spin relaxation evidences an absence of static magnetism. The remarkable observation is a scaling relation of chi[H,7] and M[H, T] in HIT with the scaling exponent alpha = 0.26-0.28, expected from bond randomness. However, C-m[H, T]/T disobeys the predicted universal scaling law, pointing towards the presence of additional low-lying excitations on the background of bond-disordered spin liquid. Our results signify a many-faceted impact of quenched disorder in a Kitaev spin system due to its peculiar bond character.