Correlations and semimetallic behaviors in pyrochlore oxide Cd ₂Re₂O₇

Electronic properties of the metallic pyrochlore oxide Cd ₂Re₂O₇ are studied by means of electrical resistivity and Hall measurements. Semimetallic band structures are revealed as expected from band structure calculations. It is found that large changes in carrier density and mass occur at the structural phase transition at T _s1 = 200 K. A large mass enhancement is observed, particularly for the high-temperature phase with the ideal pyrochlore structure, suggesting that an anomalous correlation has an important effect on the itinerant electrons in the pyrochlore lattice.