Evidences for the random singlet phase in a new honeycomb iridate SrIr$_2$O$_{6-\delta}$

TL;DR

This study provides evidence for a random singlet phase in a honeycomb iridate with disorder-induced magnetism, no magnetic order at very low temperatures, and power-law behaviors consistent with a disordered quantum spin liquid.

Contribution

It demonstrates the presence of a random singlet phase in SrIr$_2$O$_{6-eta}$, a new honeycomb iridate with oxygen vacancies, expanding the understanding of disorder effects in Kitaev-like systems.

Findings

No magnetic order observed down to 0.05 K.

Magnetic susceptibility and specific heat show power-law behavior.

Disorder from oxygen vacancies induces magnetism despite no unpaired electrons.

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 SrIr$_2$O$_{6-\delta}$ with $\delta \approx 0.25$, which consists of two-dimensional honeycomb Ir planes with edge-sharing IrO$_6$ octahedra. First-principles computation and experimental measurements suggest that the electronic system is gapped, and there should be no magnetic moment as the Ir$^{5+}$ 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 SrIr$_2$O$_{6-\delta}$, which offers a different member to the family of spin-orbital entangled iridates and Kitaev materials.