# A multiferroic two-dimensional electron gas

**Authors:** Julien Bréhin, Yu Chen, Maria D'Antuono, Sara Varotto, Daniela Stornaiuolo, Cinthia Piamonteze, Julien Varignon, Marco Salluzzo, Manuel Bibes  
**arXiv:** [2206.03843](https://arxiv.org/abs/2206.03843)  
**Date:** 2022-06-08  
**Summary page:** https://www.summarizepaper.com/en/paper/2206.03843v1/

## Key points

- Multiferroics exhibit at least two ferroic orders, such as (anti)ferromagnetism and ferroelectricity.
- Ferroelectricity is not allowed in metals, except for a few two-dimensional (semi)metals that behave as ferroelectrics.
- Researchers used x-ray spectroscopy and magnetotransport to demonstrate the coexistence of ferroelectricity and magnetism in an oxide-based two-dimensional electron gas (2DEG).
- The data showed non-volatile switching of polar displacements and anomalous Hall effect by polarization direction, indicating a magnetoelectric coupling.
- This finding provides new opportunities in quantum matter arising from the interplay between ferroelectricity, ferromagnetism, and Rashba spin-orbit coupling in a 2DEG.
- X-ray linear dichroism at the Ti L3,2 edge was measured on a sample grown using pulsed laser deposition onto Ca-STO single crystals to confirm predictions.
- DFT calculations showed larger spontaneous polarization for Pup than Pdn states.
- This study offers insights into designing novel materials with unique properties for potential applications in electronics and spintronics.

## Summary

Multiferroics are materials that exhibit at least two ferroic orders, such as (anti)ferromagnetism and ferroelectricity. While magnetic order can arise in both insulating and conducting compounds, ferroelectricity is not allowed in metals, except for a few two-dimensional (semi)metals that behave as ferroelectrics. However, the combination of magnetic order with ferroelectricity to create multiferroic metals remains elusive. In a recent study, researchers used x-ray spectroscopy and magnetotransport to demonstrate the coexistence of ferroelectricity and magnetism in an oxide-based two-dimensional electron gas (2DEG). The data showed non-volatile switching of polar displacements and anomalous Hall effect by polarization direction, indicating a magnetoelectric coupling. This finding provides new opportunities in quantum matter arising from the interplay between ferroelectricity, ferromagnetism, and Rashba spin-orbit coupling in a 2DEG. To confirm their predictions, the researchers measured X-ray linear dichroism at the Ti L3,2 edge on a sample grown using pulsed laser deposition onto Ca-STO single crystals. The element-specific technique probes local crystal field splitting and revealed red and blue spectra collected at 2 K after switching the sample into Pup and Pdn states respectively. These findings were supported by DFT calculations showing larger spontaneous polarization for Pup than Pdn states. Overall, this study offers insights into designing novel materials with unique properties for potential applications in electronics and spintronics.