Realization of a spin-liquid ground state in the high-pressure phase of Ba3YIr2O9

Ba3YIr2O9 crystallizes in a hexagonal structure and transforms into a cubic structure under an applied pressure of 8GPa at 1273K. While the ambient pressure (AP) sample undergoes long-range magnetic ordering at 4K, the high-pressure (HP) synthesized sample does not order down to 2K as evidenced from our susceptibility, heat capacity and nuclear magnetic resonance (NMR) measurements. Further, for the HP sample, heat capacity measurements demonstrate the presence of a linear term in C/T vs. T^2 in the range of 2-10K with gamma=10mJ/mol-Ir K^2. The 89Y NMR shift has no temperature (T) dependence in the range of 4-120K and spin-lattice relaxation rate varies linearly with T in the range of 8-45K (above which it is T-independent). Resistance measurements confirm that both the samples are semiconducting. Our ab-initio calculations reveal that strong spin orbit coupling (SOC) plays a crucial role in determining the magnetic and insulating properties of this system in both the phases. We suggest that the cubic (HP) phase of Ba3YIr2O9 is a 5d based, gapless, spin-liquid.