Pressure tuning of electron-phonon coupling: The insulator to metal transition in manganites

An extended temperature and pressure-dependent investigation is carried out on a La0.75Ca0.25MnO3 sample exploiting the infrared absorption technique coupled to a diamond anvil cell. The pressure dependence of the insulator to metal transition temperature T-IM is determined for the first time up to 11.2 GPa. The T-IM(P) curve we propose to model the present data has an exponential-like behavior with an associated characteristic pressure P-* playing the role of a decay constant. It is found that the equivalence between an external and an internal (chemical) pressure holds over a limited range of pressure, namely, Pless than or equal to2P(*). Moreover, a certain universality character is associated with the proposed model curve in its ability to account for a large class of low-disorder manganites characterized by intermediate electron-phonon coupling.