title: Prediction of a native ferroelectric metal.
abstract: Over 50 years ago, Anderson and Blount discussed symmetry-allowed polar distortions in metals, spawning the idea that a material might be simultaneously metallic and ferroelectric. While many studies have ever since considered such or similar situations, actual ferroelectricity--that is, the existence of a switchable intrinsic electric polarization--has not yet been attained in a metal, and is in fact generally deemed incompatible with the screening by mobile conduction charges. Here we refute this common wisdom and show, by means of first-principles simulations, that native metallicity and ferroelectricity coexist in the layered perovskite Bi5Ti5O17. We show that, despite being a metal, Bi5Ti5O17 can sustain a sizable potential drop along the polar direction, as needed to reverse its polarization by an external bias. We also reveal striking behaviours, as the self-screening mechanism at work in thin Bi5Ti5O17 layers, emerging from the interplay between polar distortions and carriers in this compound.
authors.affiliation: CNR-IOM SLACS Cagliari, Istituto Officina dei Materiali, Cittadella Universitaria, Monserrato (CA) 09042-I, Italy.
authors.forename: Alessio
authors.initials: A
authors.lastname: Filippetti
authors.affiliation: CNR-IOM SLACS Cagliari, Istituto Officina dei Materiali, Cittadella Universitaria, Monserrato (CA) 09042-I, Italy.|Dipartimento di Fisica, Universita` di Cagliari, Cittadella Universitaria, Monserrato (CA) 09042-I, Italy.
authors.forename: Vincenzo
authors.identifier: http://orcid.org/0000-0003-3794-8092
authors.initials: V
authors.lastname: Fiorentini
authors.affiliation: Dipartimento di Fisica, Universita` di Cagliari, Cittadella Universitaria, Monserrato (CA) 09042-I, Italy.|Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, 1348 Louvain-la-Neuve, Belgium.
authors.forename: Francesco
authors.initials: F
authors.lastname: Ricci
authors.affiliation: Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.|Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, 34136 Trieste, Italy.
authors.forename: Pietro
authors.identifier: http://orcid.org/0000-0003-0892-7655
authors.initials: P
authors.lastname: Delugas
authors.affiliation: Department of Materials Research and Technology, Luxembourg Institute of Science and Technology, 5 Avenue des Hauts-Fourneaux, L-4362 Esch/Alzette, Luxembourg.|Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Íñiguez