A Multiferroic Two-Dimensional Electron Gas

Multiferroics are compounds in which at least two ferroic orders coexist – typically (anti)ferromagnetism and ferroelectricity – and whose investigation has been a major area of materials science during the last two decades. While magnetic order can arise in both insulating and metallic compounds, ferroelectricity is in principle only allowed in insulators, although ferroelectric metals were proposed over 60 years ago. Recently, several two-dimensional systems have been reported to behave as ferroelectric metals. Yet, their combination with magnetic order remains elusive. In this work, we show the coexistence of ferroelectricity and magnetism in a SrTiO₃-based two-dimensional electron gas (2DEG). Ti-<i>L</i>_3,2 edge X-ray linear dichroism data evidences a modulation of the Ti-O polar displacements depending on the ferroelectric polarization direction while transport data reveal a voltage-induced hysteresis of the sheet resistance, reminiscent of the ferroelectric polarization loop. The 2DEG displays anomalous Hall effect and magnetoresistance that can both be modulated and cycled by switching the remanent polarization, demonstrating a magnetoelectric coupling. Our findings provide new opportunities in quantum matter stemming from the interplay between ferroelectricity, ferromagnetism, metallicity and Rashba spin-orbit coupling.