Flexoelectric polarizing and control of a ferromagnetic metal

Abstract

Electric polarization can only be well defined in insulators, not in metals, and there is no general scheme to induce and control bulk polarity in metals. Here, we circumvent this limitation by utilizing a pseudo-electric field generated by inhomogeneous lattice strain, namely a flexoelectric field, as a universal means of polarizing and controlling a metal. Using heteroepitaxy and atomic-scale imaging, we show that flexoelectric fields polarize the bulk of an otherwise centrosymmetric metal SrRuO3, with remarkable off-center displacements of Ru ions. This further impacts the electronic bands and lattice anisotropy of the flexo-polar SrRuO3, potentially leading to an enhancement of electron correlation, ferromagnetism, and its anisotropy. Beyond conventional electric fields, flexoelectric fields may universally engender novel electronic states and their control via pure atomic displacements.