BARELY METALLIC STATES WITH ENHANCED CARRIER MASS IN Y1-XCAXTIO3

In the nominally hole-doped Mott insulator system Y1-xCaxTiO3, the met al-insulator transition takes place near x=0.4. A thermal hysteretic b ehavior of the resistivity is observed in the immediate vicinity of th e metal-insulator phase boundary. Application of pressure tends to sup press the quasireentrant (metal-insulator-metal) transition and to sta bilize the metallic phase. Measurements of the Hall coefficient and th e electronic specific heat indicate that the barely metallic phase at about x=0.4 is characterized by an enhancement of carrier mass rather than by a reduction of carrier density.