  We have studied the low-frequency dielectric properties of the
phase-separated manganite Pr0.7Ca0.3MnO3 as a function of applied magnetic
field in the low temperature phase-separated state. The dielectric constant is
strongly field dependent and also depends on the magnetic field history of the
sample. The dielectric behavior appears to be associated with the hopping of
polaronic charge carriers, and we can derive the field dependent hopping energy
barrier from the frequency dependence of the dielectric constant. This analysis
allows us to associate the metal-insulator transition observed in this material
with the field-induced suppression of the polaron activation energy.
