Evidence for the random singlet phase in the honeycomb iridate SrIr2O6

Abstract

Strong spin-orbital-coupling magnetic systems with the honeycomb structure can provide bond-directional interactions which may result in Kitaev quantum spin liquids and exotic anyonic excitations. However, one of the key ingredients in real materials - disorders - has been much less studied in Kitaev systems. Here we synthesized a trigonal SrIr2O6-δ with δ≈0.25, which consists of two-dimensional honeycomb Ir planes with edge-sharing IrO6 octahedra. First-principles computation and experimental measurements suggest that the electronic system is gapped, and there should be no magnetic moment as the Ir5+ ion has no unpaired electrons. However, significant magnetism has been observed in the material, and it can be attributed to disorders that are most likely from oxygen vacancies. No magnetic order is found down to 0.05 K, and the low-temperature magnetic properties exhibit power-law behaviors in magnetic susceptibility and zero-field specific heat, and a single-parameter scaling of the specific heat under magnetic fields. These results provide strong evidence for the existence of the random singlet phase in SrIr2O6-δ, which offers a different member to the family of spin-orbital entangled iridates and Kitaev materials. © 2021 American Physical Society.