Quantum spin liquid ground state in Ba₃InIr₂O₉. A combined NMR and μSR study

5d Iridium based systems have drawn a lot of attention because of the presence of similar energy scales of crystal field splitting, spin-orbit coupling and on-site Coulomb interaction which give rise to unconventional ground states. In the present compound Ba₃InIr₂O₉ (Ir has an average of +4.5 oxidation state), Ir-dimers aligned along crystallographic c-axis form a triangular lattice which promotes frustration. The magnetization and specific heat show no evidence of long-range magnetic ordering down to 400 mK. We have employed ¹¹⁵In (I=9/2) NMR and μSR to study the microscopic nature of the ground state. ¹¹⁵In Knight shift and line width exhibit a temperature independent behavior below 1.4 K down to 25 mK which indicates no static correlations are developing down to such a low temperature whereas the nuclear spin-lattice relaxation rate (1/T₁) shows a dynamical behavior in the same temperature range and follows a T^2.2 power law. Furthermore, we have carried out μSR experiments which also discarded the presence of any static long-range ordering and provide the evidence of dynamical fluctuations down to 25 mK. Altogether, local probes provide strong evidence for gapless quantum spin liquid ground state in Ba₃InIr₂O₉.