Polar metals with coexisting ferroelectricity and high-density conduction electrons

Polar metals, a family of materials with exclusive but coexisting electric polarization and metallicity, have attracted plenty of studies recently. Experimentally, how these two exclusive states interact with each other is still an open question thus far. Here, we report on the existence of ferroelectric metal states with switchable electric polarization and unexpected high carrier density in Ba0.5La0.5TiO3 films. A combination of atomic resolution scanning transmission electron microscopy, high-resolution x-ray diffraction, piezoresponse force microscopy, optical second harmonic generation, and electrical transport was utilized to investigate the crystal and electronic structures of Ba0.5La0.5TiO3 films. Unexpectedly, with the modulation of ferroelectricity, the density of conduction electrons can be tuned from 1019 to 1021 cm−3. Our results provide a way to design polar metals with coexisting switchable electric polarization and high-density conduction electrons.