Superconductivity in a pyrochlore oxide, Cd2Re2O7

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Abstract
We make the first report that a metallic pyrochlore oxide, Cd2Re2O7, exhibits type II superconductivity at 1.1 K. The pyrochlore oxide is known to be a geometrically frustrated system, which includes a tetrahedral network of magnetic ions. A large number of compounds are classified in the family of pyrochlore oxides, and these compounds exhibit a wide variety of physical properties ranging from insulator through semiconductor and from bad metal to good metal. Until now, however, no superconductivity has been reported for frustrated pyrochlore oxides. The bulk superconductivity of this compound is confirmed by measurements of the resistivity and the alternating-current magnetic susceptibility. The upper critical field Hc2, which is extrapolated to 0 K, is estimated as about 0.8 T, using the resistivity measurements under an applied field. The plot of Hc2 versus T indicates that the Cooper pairs are composed of rather heavy quasiparticles. This fact suggests that frustrated heavy electrons become superconducting in this compound.