How ice enables superconductivity in Na_xCoO₂· yH₂O by melting charge order: possibility of novel electric field effects

Abstract

Charge ordering in doped CoO₂ planes near the commensurate fillings x =¼ and 1/3 are considered for Na_xCoO₂ · yH₂O and suggested to be competitors to superconductivity, leading to the experimentally seen narrow superconducting dome bounded by commensurate doping: 1/4 > x > 1/3. Intercalated hydrogen bonded H₂O network, by its enhanced dielectric constant, screen and frustrate local charge order condensation energy and replace a generic 'charge glass order' by superconductivity in the dome. An access to superconductivity and charge order, available through the new water channel, is used to predict novel effects such as 'Electrical Modulation of Superconductivity' and 'Electroresistance Effect'.