Superconductivity of heavy carriers in the pressure-induced phases of Cd₂Re₂O₇

The superconductivity of Cd₂Re₂O₇ is investigated under hydrostatic pressures up to 4.6 GPa by means of electrical resistivity. A rich phase diagram is obtained, which contains at least five new pressure-induced phases in addition to the three already present at ambient pressure, revealing inherent structural and electronic instabilities of the compound. We find large enhancements of more than one order of magnitude in the upper critical field as well as in the coefficient of the T² term in resistivity at around a critical pressure of 4.2 GPa, where an inversion-symmetry-breaking structural transition tends to disappear. Heavy fermion superconductivity is probably realized under high pressures in Cd ₂Re₂O₇, which is extraordinary for d-electron compounds.