Artificial two-dimensional ferroelectric metal at room temperature*

Polar metals, commonly defined by the coexistence of polar crystal structure and metallicity, are thought to be scarce because the long-range electrostatic fields 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 ferroelectric metal in a tri-color superlattice BaTiO3/SrTiO3/LaTiO3. A combination of advanced probes and DFT calculations have revealed the microscopic mechanisms of unusual periodic electric polarization, charge distribution, and orbital symmetry. Our results provide a route to create all-oxide artificial non-centrosymmetric quasi-two-dimensional metals with exotic quantum and topological states including potentially coexisting ferroelectric, ferromagnetic, and superconducting phases.