Superconductivity in the Frustrated-Spin System Cd₂Re₂O₇ with Pyrochlore Structure

Abstract

Newly found superconductor Cd₂Re₂O₇ with the Pyrochlore lattice structure is introduced in terms of frustrated-spin system. This superconductor is of the second-kind with the critical temperature T_c=1.1 K and the upper critical field H_c2=0.8 T. Furthermore, this compound has been found to exhibit the structural transition around T^*=200 K, in which the alternating tetramerization is formed in the Pyrochlore lattice. The spin-gap type nuclear relaxation has been observed below this transition, which may be concerned with the change of the electronic states as well as the occurrence mechanism of the superconductivity in this system. The superconducting properties of Cd₂Re₂O₇ are explained, then the structural transition and Cd NMR results in the normal state will be reported.