  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 new trigonal SrIr$_2$O$_6$, which
consists of two-dimensional honeycomb Ir planes with edge-sharing IrO$_6$
octahedra. First-principle 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 evidences for the existence of the random singlet phase in
SrIr$_2$O$_6$, which offers a new member to the family of spin-orbital coupled
iridates and Kitaev materials.
