Ferroelectricity in underdoped La-based cuprates

TL;DR

This study reveals that ferroelectricity and magnetoelectric coupling are common in underdoped La-based cuprates, arising from local structural distortions caused by doping, which may shed light on the complex electronic phases in high-Tc superconductors.

Contribution

It demonstrates the presence of ferroelectricity and magnetoelectric coupling in multiple La-214 cuprates, linking these phenomena to local structural distortions and doping effects.

Findings

Ferroelectricity is observed in La-214 cuprates with different dopants.

Magnetoelectric coupling can be tuned via Dzyaloshinskii-Moriya interaction.

Ferroelectricity likely originates from local CuO6 octahedral distortions.

Abstract

Doping a parent antiferromagnetic Mott insulator in cuprates leads to short-range electronic correlations and eventually to high-Tc superconductivity. However, the nature of charge correlations in the lightly doped cuprates remains unclear. Understanding the intermediate electronic phase in the phase diagram (between the parent insulator and the high-Tc superconductor) is expected to elucidate the complexity both inside and outside the superconducting dome, and in particular in the underdoped region. One such phase is ferroelectricity whose origin and relation to the properties of high-Tc superconductors is subject of current research. Here we demonstrate that ferroelectricity and the associated magnetoelectric coupling are in fact common in La-214 cuprates namely, La$_{2-x}$Sr$_x$CuO$_4$, La$_2$Li$_x$Cu$_{1-x}$O$_4$ and La$_2$CuO$_{4+x}$. It is proposed that ferroelectricity results from local CuO$_6$ octahedral distortions, associated with the dopant atoms and/or clustering of the doped charge carriers, which break spatial inversion symmetry at the local scale whereas magnetoelectric coupling can be tuned through Dzyaloshinskii-Moriya interaction.