Filippetti Alessio, Fiorentini Vincenzo, Ricci Francesco, Delugas Pietro, Íñiguez Jorge
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.
Nat Commun. 2016 Apr 4;7:11211. doi: 10.1038/ncomms11211.
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.
五十多年前，安德森和布朗特讨论了金属中对称性允许的极性畸变，由此催生了一种观点，即一种材料可能同时具有金属性和铁电性。自那时起，虽然许多研究都考虑过此类或类似情况，但金属中尚未实现实际的铁电性，也就是说，尚未实现可切换的本征电极化的存在，实际上，人们普遍认为这与可移动传导电荷的屏蔽作用不相容。在此，我们驳斥了这一普遍观点，并通过第一性原理模拟表明，层状钙钛矿Bi5Ti5O17中天然金属性和铁电性共存。我们表明，尽管Bi5Ti5O17是一种金属，但它能够沿极性方向维持可观的电势降，这是通过外部偏压反转其极化所必需的。我们还揭示了一些引人注目的行为，比如在薄Bi5Ti5O17层中起作用的自屏蔽机制，它源于该化合物中极性畸变与载流子之间的相互作用。
