Magnetism, structure, and superconductivity of Cd 2Re 2O 7 pyrochlore: Cd and Re NMR

Abstract

We present Cd and Re NMR results on Cd 2Re 2O 7, the first and as yet the only superconductor (T c ≃1 K) among pyrochlore oxides. Re spin-lattice relaxation rate below T c exhibits a pronounced coherence peak and follows the weak-coupling BCS with nearly isotropic energy gap. Cd NMR points to moderate ferromagnetic enhancement at high temperatures followed by rapid decrease of the density of states below 200 K , and to strong suppression of spin fluctuations below ∼75 K . Cd and Re NMR spectra reveal two structural phase transitions, one at 200 K and another at 120 K . Re NQR rules out any magnetic or charge order.