Metallic ferroelectricity induced by anisotropic unscreened Coulomb interaction inLiOsO3

Abstract

As the first experimentally confirmed ferroelectric metal, LiOsO3 has received extensive research attention recently. Using density-functional calculations, we perform a systematic study on the origin of the metallic ferroelectricity in LiOsO3. We confirm that the ferroelectric transition in this compound is order-disorder like. In addition, we find that the distribution of the conduction electron is extremely anisotropic, which suggests that the electric screening ability is also highly anisotropic. Then, by doing electron screening analysis, we unambiguously demonstrate that the long range ferroelectric order in LiOsO3 results from the incomplete screening of the dipole-dipole interaction along the nearest neighboring Li-Li chain direction. We therefore conclude highly anisotropic screening and local dipole-dipole interactions are two most important keys to form LiOsO3-type metallic ferroelectricity. 72.80.Ga, 61.50.Ah The ferroelectric (FE) instability can be explained by a delicate balance between short-range elastic restoring forces supporting the undistorted paraelectric (PE) structure and long-range Coulomb interactions favoring the FE phase [1]. Itinerant electrons can screen the electric fields and inhibit the electrostatic forces, metallic systems are thus not expected to exhibit ferroelectric like structural distortion. Despite the incompatibility, using a phenomenological theory, Anderson and Blount proposed in 1965 that metals can break inversion symmetry [2]. They found that the FE metal is possible through a continuous structural transition accompanied by the appearance of a polar axis, and the disappearance of an inversion center [2]. In 2004, Cd 2 Re 2 O 7 had been proposed as a rare example of ferroelectric metals [3], however, it was found that although this compound exhibits a second order phase transition to a structure that lacks inversion symmetry, a unique polar axis could not be identified [4], which does not fit the criteria about the FE metal.Very recently, the first convincing success was achieved experimentally in LiOsO 3 [1]. LiOsO 3 remains metallic behavior while it undergoes a second-order phase transition from the high temperature centrosymmetric R3c to a FE-like R3c structure at T s = 140K [1]. Neutron and xray diffraction studies showed that the structural phase transition involves the displacements of Li ions accompanying also a slight shift of O ions [1]. The electronic structure and lattice instability were studied by several groups [6][7][8]. It was found that the local polar distortion in LiOsO 3 is solely due to the instability of the A-site Li ion [6][7][8]. The importance of the Coulomb interaction among 5d electrons and the hybridization between oxygen p orbitals and Os empty e g orbitals has also been emphasized by Giovannetti and Capone[8]. Despite these efforts devoted to understanding the origin of the FE like structural transition in this metallic system, there are still two fundamental issues have not been clearly clarified. The first is the origin of the fer...

Strain-Engineered Multiferroicity inPnmaNaMnF3Fluoroperovskite

“…La 2 NiMnO 6 [15]) and "ferroelectric metals" (e.g. LiOsO 3 [16,17]) involving a A-site dominated effect, but it is different to the A-site stereochemically active lone pair origin observed in some oxides (e.g. PbTiO 3 or BiFeO 3 ) oxides and to the phonon mode coupling origin present in improper and hybrid-improper FE [18].…”

“…The computed linear piezoelectric coefficients e 21 , e 23 , e 22 , e 16 , and e 34 at 0% strain are equal to 1.010, -0.672, 0.064, -0.108, and 0.058 C·m −2 respectively and are not far from the ones observed in BaTiO 3 [32,33]. From the quadratic fitting observed in Fig 2, we can extract that the overall non-linear contribution related to the sum of the B µjk components and we found it to be about 60% of the linear piezoelectric constants (e µj ).…”

Electronic correlations in the ferroelectric metallic state ofLiOsO3

“…First theoretical insights about the mechanism behind the ferroelectric instability and the metallic character of LiOsO 3 were gained by using Density Functional Theory (DFT) calculations [3][4][5]. The ferroelectric transition in metallic LiOsO 3 mainly results from the cooperative displacements of Li and O ions, while the metallic conduction is associated with the t 2g orbitals of osmium which are partially occupied by three electrons per ion [4].…”

Theoretical studies of all-electric spintronics utilizing multiferroic and magnetoelectric materials

“…The strain effect in tetragonal SrRuO 3 might be used to tune the physical properties of MTJs. We should point out that the SrRuO 3 under strain could also be called ferroelectric metal, but may have different mechanism from that of LiOsO 3 [34,35]. The relevant study is currently on the way.…”