Quantum frustration in the ''spin liquid" phase of two-dimensional He-3

We have measured the ultralow temperature and low field magnetic susceptibi lity of the 4/7 phase of two-dimensional He-3 adsorbed on graphite preplate d by one layer of He-4. The experiments art performed by progressively addi ng He-4 to the system, thus suppressing in a controlled way the He-3 atoms trapped in substrate heterogeneities. This procedure enables us to determin e the intrinsic properties of this spin, model magnet in the zero field lim it. The results show quantitatively that the system is strongly frustrated by multiple spin exchange interactions. A characteristic gapped spin liquid behavior is observed at ultralow temperature.