Flexoelectric control of a ferromagnetic metal

TL;DR

This paper demonstrates that flexoelectric fields, generated by inhomogeneous strain, can polarize and modify the properties of a metallic oxide, SrRuO3, revealing a new method to control electronic states in metals.

Contribution

It provides the first experimental evidence that flexoelectric fields can induce polarization and lattice changes in a metal, enabling novel control of electronic and magnetic properties.

Findings

Flexoelectric fields polarize SrRuO3 with large Ru off-center displacements.

Flexoelectric-induced polarization causes significant lattice expansion.

Potential enhancement of ferromagnetism through flexoelectric-driven atomic displacements.

Abstract

Electric fields have played a key role in discovering and controlling exotic electronic states of condensed matter. However, electric fields usually do not work in metals as free carriers tend to screen electrostatic fields. While a pseudo-electric field generated by inhomogeneous lattice strain, namely a flexoelectric field, can in principle work in all classes of materials, it remains experimentally unexplored in metals. Here, using heteroepitaxy and atomic-scale imaging, we show that flexoelectric fields can polarize a metallic oxide SrRuO3 with unexpectedly large Ru off-center displacements. We also observe that the flexoelectrically induced polar state of SrRuO3 leads to sizable lattice expansion, similar to the electrostrictive expansion caused by ionic displacements in dielectrics under an external electric field. We further suggest that flexoelectrically driven Ru off-centering promotes strong coupling between lattice and electronic degrees of freedom, possibly enhancing the ferromagnetism of SrRuO3. Beyond conventional electric fields, flexoelectric fields may universally engender novel electronic states and their control via pure atomic displacements in a nondestructive and fast manner.