Superconductivity and Ferroelectricity
Résumé
Superconductivity and ferroelectricity appear at first sight as mutually exclusive phenomena. Indeed, the local electric fields generated by the dipoles at the heart of ferroelectricity should be screened by conduction electrons. Therefore, ferroelectrics and conductive materials should compose two non-overlapping sets of materials. The incompatibility between ferroelectricity and superconductivity was further reinforced from
symmetry argument, the so-called “Matthias conjecture”. 1
Fifty years ago though, Anderson and Blount predicted the possibility of a ferroelectriclike transition in metals.2 Motivated by the recent experimental verification that such amaterial exists3 and the observation of ferroelectricity in underdoped La2CuO4+x4, we undertook to review the question of ferroelectricity and superconductivity.
After briefly recalling some examples of ferroelectrics, which, once doped or reduced,become superconductors, we shall give an overview of the recent experimental observations of ferroelectric (or ferroelectric-like) behavior in high-TC superconductors, including magnetoelectricity.5
Then, the various approaches used to tackle the two phenomena within a common framework shall be presented, motivated by the possible increase in TC that may result from the enhancement of the electron-phonon coupling due to the soft-mode behavior of displacive
ferroelectrics.
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