Artificial two-dimensional polar metal at room temperature

TL;DR

This paper reports the creation of a room-temperature two-dimensional polar metal in oxide superlattices, demonstrating coexistence of polarization and metallicity at the atomic scale, opening pathways for exotic quantum states.

Contribution

It introduces a novel all-oxide 2D polar metal at room temperature, combining experimental and theoretical methods to understand its microscopic mechanisms.

Findings

Realization of a room-temperature 2D polar metal in oxide superlattices

Atomic-scale imaging reveals polarization and charge distribution

Potential for exotic quantum states like ferroelectricity and superconductivity

Abstract

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.