Low-temperature ferroelectric phase and magnetoelectric coupling in the   underdoped La_2CuO_(4+x)
  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. 
Z. Viskadourakis, I. Radulov, A. P. Petrovi\'c, S. Mukherjee, B. M.   Andersen, G. Jelbert, N.S. Headings, S.M. Hayden, K. K...
cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el