Polar metal phase stabilized in strained La-doped BaTiO 3 films

• Published in: Scientific reports Vol. 7; no. 1; p. 4631
• Main Authors: Takahashi, K S, Matsubara, Y, Bahramy, M S, Ogawa, N, Hashizume, D, Tokura, Y, Kawasaki, M
• Format: Journal Article
• Language: English
• Published: England 01.12.2017
• ISSN: 2045-2322
• DOI: 10.1038/s41598-017-04635-3

Ferroelectric polarization and metallic conduction are two seemingly irreconcilable properties that cannot normally coexist in a single system, as the latter tends to screen the former. Polar metals, however, defy this rule and have thus attracted considerable attention as a new class of ferroelectrics exhibiting novel properties. Here, we fabricate a new polar metal film based on the typical ferroelectric material BaTiO by combining chemical doping and epitaxial strain induced by a substrate. The temperature dependences of the c-axis lattice constant and the second harmonic generation intensity of La-doped BaTiO films indicate the existence of polar transitions. In addition, through La doping, films become metallic at the polar phase, and metallicity enhancement at the polar state occurs in low-La-doped films. This intriguing behaviour is effectively explained by our first-principles calculations. Our demonstration suggests that the carrier doping to ferroelectric material with epitaxial strain serves as a new way to explore polar metals.