Kinetic Energy Driven Superconductivity in the Electron Doped Cobaltate NaxCoO2·yH2O

Within the charge-spin separation fermion--spin theory, we show that the mechanism of superconductivityin the electron doped cobaltate NaCoO2·yHO is ascribed to its kinetic energy. The dressed fermions interact occurringdirectly through the kinetic energy by exchanging magnetic excitations. This interaction leads to a net attractive forcebetween dressed fermions, then the electron Cooper pairs origimating from the dressed fermion pairing state are due tothe charge-spin recombination, and their condensation reveals the superconducting ground state. The superconductingtransition temperature is identical to the dressed fermion pair transition temperature, and is suppressed to a lowertemperature due to the strong magnetic frustration. The optimal superconducting transition temperature occurs in theelectron doping concentration δ≈0.29, and then decreases for both underdoped and overdoped regimes, in qualitativeagreement with the experimental results.