Cd and Re NMR/NQR in pyrochlore compound Cd2Re2O7 Original Research Article

We report a nuclear magnetic/quadrupole resonance study of phase transitions in Cd2Re2O7, specifically the structural transition at ∼200 K and the superconducting one at ∼1 K. Single crystal 111Cd NMR spectra infer a second-order structural transition at ∼200 K. Splitting of the Cd NMR lines below 200 K, as well as asymmetric electric field gradient obtained from 185/187Re NQR spectra, point to lack of the three-fold symmetry around [111] direction for these sites. No magnetic order has been found at low temperature. Below 1 K, the zero-field (NQR) spin–lattice relaxation rate of 187Re exhibits a large coherence peak and behaves within the weak-coupling BCS model with a nearly isotropic energy gap.