Na2V3O7: An unusual low-dimensional quantum magnet

Results of present and previous measurements of the 23Na NMR response, dc- and ac-magnetic susceptibilities and the specific heat of Na2V3O7 at low temperatures suggest that this material is close to a quantum critical point (QCP) at μ0H=0T. The experimental data can be explained by assuming that below 100K the localized V magnetic moments (S=12) form a collection of dimers, with a broad distribution of singlet-triplet gaps. Most of the dimers adopt a singlet ground state with gaps between 0 and 350K. A small fraction of them forms triplet ground states with gaps between 0 and 15K. The degeneracy of the triplet ground states is lifted by a phase transition at an unusually low temperature of 0.086K. Modest magnetic fields effectively quench this low-temperature state and the system is driven away from the QCP as the applied fields are enhanced to above 1T