  Electronic properties of the metallic pyrochlore oxide Cd2Re2O7 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 Ts1 = 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.
