Low-temperature ferroelectric phase and magnetoelectric coupling in the underdoped La_2CuO_(4+x)

TL;DR

This study uncovers a low-temperature ferroelectric phase and magnetoelectric coupling in highly underdoped La_2CuO_(4+x), revealing spin-charge interactions and polar nanoregions in a parent high-temperature superconductor.

Contribution

It demonstrates the existence of ferroelectricity and magnetoelectric effects in underdoped La_2CuO_(4+x), a novel finding in high-temperature cuprate superconductors.

Findings

Ferroelectric ground state below 4.5 K

Anisotropic magnetoelectric response observed

Charge dynamics develop below 40 K

Abstract

We report the discovery of a ferroelectric ground state below 4.5 K in highly underdoped La_2CuO_(4+x) accompanied by slow charge dynamics which develop below T~40 K. An anisotropic magnetoelectric response has also been observed, indicating considerable spin-charge coupling in this lightly doped "parent" high temperature copper-oxide superconductor. The ferroelectric state is proposed to develop from polar nanoregions, in which spatial inversion symmetry is locally broken due to non-stoichiometric carrier doping.