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

We have measured the ultralow temperature and low field magnetic susceptibility of the 4/7 phase of two-dimensional He-3 adsorbed on graphite preplated by one layer of He-4. The experiments art performed by progressively adding He-4 to the system, thus suppressing in a controlled way the He-3 atoms trapped in substrate heterogeneities. This procedure enables us to determine the intrinsic properties of this spin, model magnet in the zero field limit. 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.