Decrease in 111Cd Knight Shift in Superconducting Cd2Re2O7: Evidence for Spin-Singlet Pairing

111 Cd NMR measurements have been performed in the superconducting (SC) state of the pyrochlore Cd 2 Re 2 O 7 at T c ∼1 K, and in a field of less than 3 kOe below T c . The upper critical field at 0.1 K has been determined to be 4 kOe from in situ measurements of the ac susceptibility. A reduction of the Knight shift in the SC state is confirmed. The present results provide strong evidence that this compound has a singlet SC pairing symmetry.