Above – This image shows the positions of atoms in a ferroelectric-like metal that contains barium titanate, strontium titanate and lanthanum titanate. Image: Zhen Wang and Yimei Zhu; image obtained at Brookhaven National Laboratory
A cornerstone of technology, ferroelectric materials are used in electronics such as cell phone and other antennas, computer storage, medical equipment, high precision motors, ultra-sensitive sensors and sonar equipment. None of their materials conducts electricity and the Rutgers-led findings potentially could spawn a new generation of devices and applications.
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 BaTiO3/SrTiO3/LaTiO3. 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.