Barely metallic states with enhanced carrier mass in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{TiO}}_3$

In the nominally hole-doped Mott insulator system ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ca}}_{\mathit{x}}$ ${\mathrm{TiO}}_3$, the metal-insulator transition takes place near x=0.4. A thermal hysteretic behavior of the resistivity is observed in the immediate vicinity of the metal-insulator phase boundary. Application of pressure tends to suppress the quasireentrant (metal-insulator-metal) transition and to stabilize the metallic phase. Measurements of the Hall coefficient and the 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.