Strain-induced metal-insulator phase coexistence in perovskite manganites

The coexistence of distinct metallic and insulating electronic phases within the same sample of a perovskite manganite(1-6), such as La1-x-yPryCaxMnO3, presents researchers with a tool for tuning the electronic properties in materials. In particular, colossal magnetoresistance(7) in these materials - the dramatic reduction of resistivity in a magnetic field - is closely related to the observed texture owing to nanometre- and micrometre-scale inhomogeneities(1) (-6,8). Despite accumulated data from various high-resolution probes, a theoretical understanding for the existence of such inhomogeneities has been lacking. Mechanisms invoked so far, usually based on electronic mechanisms and chemical disorder(9-11), have been inadequate to describe the multiscale, multiphase coexistence within a unified picture. Moreover, lattice distortions and long-range strains(12,13) are known to be important in the manganites(14). Here we show that the texturing can be due to the intrinsic complexity of a system with strong coupling between the electronic and elastic degrees of freedom. This leads to local energetically favourable configurations and provides a natural mechanism for the self-organized inhomogeneities over both nanometre and micrometre scales. The framework provides a physical understanding of various experimental results and a basis for engineering nanoscale patterns of metallic and insulating phases.