Switching a polar metal via strain gradients

Although rare, spontaneous breakdown of inversion symmetry sometimes occurs in a material which is metallic: these are commonly known as polar metals or ferroelectric metals. Their “polarization”, however, is difficult to switch via an electric field, which limits the experimental control over band topology. Here we shall investigate, via first-principles theory, flexoelectricity as a possible way around this obstacle with the well known polar metal LiOsO₃ . The flexocoupling coefficients are computed for this metal with high accuracy with an approach based on real-space sums of the interatomic force constants. A Landau-Ginzburg-Devonshire-type first-principles Hamiltonian is built and a critical bending radius to switch the material is estimated, whose order of magnitude is comparable to that of BaTiO₃. Our work opens exciting new avenues in the search for new functionalities in polar metals, and in the field of flexoelectricity too. Our results constitute the first successful calculation of flexocoupling coefficients in metals, and constitutes therefore an important advance in first-principles methodologies as well.