Observation of a Room Temperature Two-dimensional Ferroelectric Metal

TL;DR

This paper reports the creation of a two-dimensional ferroelectric metal at room temperature by engineering superlattices that combine ferroelectric polarization with metallic conductivity, challenging traditional notions of mutual exclusivity.

Contribution

The study demonstrates the synthesis of a 2D ferroelectric metal through superlattice engineering, showing coexistence of ferroelectricity and metallicity at room temperature.

Findings

Ferroelectric polarization observed in atomically thin SrRuO3 layers.

Metallic conductivity coexists with ferroelectricity in the superlattices.

Structural and electronic analyses confirm the coexistence of properties.

Abstract

Materials with reduced dimensions have been shown to host a wide variety of exotic properties and novel quantum states that often defy textbook wisdom1-5. Ferroelectric polarization and metallicity are well-known examples of mutually exclusive properties that cannot coexist in bulk solids because the net electric field in a metal can be fully screened by free electrons6. An atomically thin metallic layer capped by insulating layers has shown decent conductivity at room temperature7. Moreover, a penetrating polarization field can be employed to induce an ion displacement and create an intrinsic polarization in the metallic layer. Here we demonstrate that a ferroelectric metal can be artificially synthesized through imposing a strong polarization field in the form of ferroelectric/unit-cell-thin metal superlattices. In this way the symmetry of an atomically thin conductive layer can be broken and manipulated by a neighboring polar field, thereby forming a two-dimensional (2D) ferroelectric metal. The fabricated of (SrRuO3)1/(BaTiO3)10 superlattices exhibit ferroelectric polarization in an atomically thin layer with metallic conductivity at room temperature. A multipronged investigation combining structural analyses, electrical measurements, and first-principles electronic structure calculations unravels the coexistence of 2D electrical conductivity in the SrRuO3 monolayer accompanied by the electric polarization. Such 2D ferroelectric metal paves a novel way to engineer a quantum multi-state with unusual coexisting properties, such as ferroelectrics, ferromagnetics and metals, manipulated by external fields8,9.