Pressure induced insulator-metal phase transition on Pr_0.6Ca_0.4MnO₃ thin films

We report low-temperature Raman measurements under hydrostatic pressure in Pr_0.6Ca_0.4MnO₃ thin films grown on LaAlO₃ substrate. Certain phonons attributed to metallic rhombohedral phase become narrower with pressure and coexist with broad bands characteristic of spectra from the insulating paramagnetic orthorhombic phase. This behavior is similar with the changes induced from the chemical pressure (Ca substitution) and has been attributed to ferromagnetic metallic clusters formed in the insulating phase. Our data indicate that the Jahn-Teller distortion of the octahedra and the transition temperature is reduced under pressure.