Quantum critical behavior in the 1D Heisenberg linear chain system Rb$_{2}$PbCu(NO$_{2}$)$_{6}$*

The quantum critical region of the phase diagram of the 1D spin ½ Heisenberg linear chain system Rb$_{2}$PbCu(NO$_{2}$)$_{6}$ has been investigatred using $^{87}$Rb NMR measurements on a polycrystalline sample. The low J value (2.6 K) leads to a low value for the saturation field.The $^{87}$Rb frequency shifts and spin-lattice relaxation rates, determined as a function of temperature and applied field, provide information on the transition to the Tomanaga-Luttinger-liquid phase. Scaling behavior in accordance with quantum criticality is examinerd.