Pressure-Induced Polaronic to Itinerant Electronic Transition inLa1−xSrxMnO3Crystals

Measurements of the temperature dependence of the resistivity $\rho \left(T\right)$ and thermoelectric power $\alpha \left(T\right)$ under several hydrostatic pressures were made on single crystals of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ with $x=0.12\mathrm{}$ and 0.15 in which charge ordering takes place below $T_{\mathrm{co}}$. We report a transition from the polaronic to an itinerant electronic state in the pressure range $5<P<\mathrm{}6\mathrm{}\mathrm{kbar}$ in the $x=0.15\mathrm{}$ sample. The polaronic state is modeled as a mobile three-manganese cluster within a matrix of dynamic Jahn-Teller deformations at Mn(III) ions.