Luttinger liquid behavior in the alternating spin-chain system copper nitrate.

We determine the phase diagram of copper nitrate Cu(NO3)2 . 2.5D2O in the context of quantum phase transitions and novel states of matter. We establish this compound as an ideal candidate to study quasi-ID Luttinger liquids, 3D Bose-Einstein-Condensation of triplons, and the crossover between ID and 3D physics. Magnetocaloric effect, magnetization, and neutron scattering data provide clear evidence for transitions into a Luttinger liquid regime and a 3D long-range ordered phase as a function of held and temperature. Theoretical simulations of this model material allow us tofully establish the phase diagram and to discuss it in the context of dimerized spin systems. [ABSTRACT FROM AUTHOR]