Journal Article

Artificial two-dimensional polar metal at room temperature

Gopalan, Venkatraman, Cao, Yanwei, Wang, Zhen, Park, Se Young, Meyers, D., Nikitin, Sergey M., Zhu, Yimei, Thompson, P., Chakhalian, J., Ryan, P. J., Shafer, Padraic, Akamatsu, Hirofumi, Liu, Xiaoran, Arenholz, E., Kareev, M., Rabe, Karin M., Middey, S., Yuan, Yakun, N’Diaye, A.

2018

Overview

Polar metals, commonly defined by the coexistence of polar crystal structure and metallicity, are thought to be scarce because the long-range electrostatic fields favoring the polar structure are expected to be fully screened by the conduction electrons of a metal. Moreover, reducing from three to two dimensions, it remains an open question whether a polar metal can exist. Here we report on the realization of a room temperature two-dimensional polar metal of the B-site type in tri-color (tri-layer) superlattices BaTiO 3 /SrTiO 3 /LaTiO 3 . A combination of atomic resolution scanning transmission electron microscopy with electron energy-loss spectroscopy, optical second harmonic generation, electrical transport, and first-principles calculations have revealed the microscopic mechanisms of periodic electric polarization, charge distribution, and orbital symmetry. Our results provide a route to creating all-oxide artificial non-centrosymmetric quasi-two-dimensional metals with exotic quantum states including coexisting ferroelectric, ferromagnetic, and superconducting phases. Materials that combine metallic behaviour with stable electric polarization are scarce despite being proposed in the 1960s. Here the authors engineer a perovskite heterostructure where 2D polar metallic behavior coexists with built-in electric polarization from the displacement of B-site titanium cations.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 140/146 / 142/136 / 639/301/357/995 / 639/766/119/544 / Atomic structure / Barium titanates / Charge distribution / Coexistence / Conduction / Conduction electrons / Crystal structure / Design / Electric fields / Electric polarization / Electric power distribution / Electron energy / Electrostatic properties / Energy transmission / Ferroelectric materials / Ferroelectricity / Ferromagnetism / First principles / Humanities and Social Sciences / Laboratories / Materials science / Metallicity / Metals / multidisciplinary / Physics / Room temperature / Scanning electron microscopy / Scanning transmission electron microscopy / Science / Science (multidisciplinary) / Second harmonic generation / Spectroscopy / Spectrum analysis / Superconductivity / Superlattices / Symmetry / Thin films / Transmission electron microscopy