NMR probe of spin gap characteristics in Cu$_{2}$Sc$_{2}$Ge$_{4}$O$_{13}$

We report the results of a $^{45}$Sc nuclear magnetic resonance (NMR) study on the quasi-one-dimensional compound Cu$_{2}$Sc$_{2}$Ge$_{4}$O$_{13}$ at temperatures between 4 K and 300 K. This material has been a subject of current interest due to indications of spin gap behavior. The temperature-dependent NMR shift exhibits a character of low-dimensional magnetism with a negative broad maximum at $T_{max} \quad \sim $ 170 K. Below $T_{max}$, the NMR shifts and spin lattice relaxation rates clearly show activated responses, confirming the existence of spin gap in Cu$_{2}$Sc$_{2}$Ge$_{4}$O$_{13}$. The observed data can be well fit to the spin dimer model, yielding a spin gap value of about 275 K. A detailed analysis indicates that the nearly isolated dimer picture is proper for the understanding of gap feature in this material.