Pressure effects on the metal-insulator transition in magnetoresistive manganese perovskites

Quasi-hydrostatic-pressure measurements of electrical resistivity up to 11 kbar are presented for a series of manganese perovskites L2/3A1/3MnO₃. It is found that the Curie temperature TC, being itself a function of the electronic bandwidth $W,$ displays a larger variation of dlnTC/dP as the bandwidth is reduced. It is shown that this effect arises primarily from the Mn-O-Mn bond stretching under pressure. However, the observed dlnTC/dP versus TC or W variations are found to be significantly larger than expected on the basis of simple steric modifications of bandwidth. We suggest that the electron-phonon coupling is substantially reduced under pressure; this effect is more prominent as the bandwidth is reduced.