Highlights•The nonmagnetic effect in Gossamar superconductors.•Gutzwiller projected mean-field approximation and Bogoliubov-de Gennes theory.•The particle–hole asymmetry tunneling spectrum.•The evolution of impurity-induced resonance states with the electron correlations.The local density of states (LDOS) around a nonmagnetic impurity in Gossamer superconductors has been studied based on the two-dimensional t–U–J model. Within the Gutzwiller projected mean-field approximation and Bogoliubov-de Gennes theory, the order parameters are determined in a self-consistent way, and the main related experimental results are reproduced. In the large U limit without electron double occupancy, the impurity induced quasiparticle resonance states appear at low energies, at the same time the asymmetric superconducting coherence peaks are strongly suppressed. With increasing double occupancy number d which is modulated by the Coulomb repulsion U, the order parameter gradually decreases, while the impurity induced resonance states always survive, then move to the Fermi energy and merge into a single resonance peak when the double occupancy d is big enough. These features mean for different superconducting compounds with or without strong electron correlation, the impurity induced resonance states may vary, strongly suggesting the role played by the electron correlation in cuprate superconductors.

We study the interplay between superconductivity and antiferromagnetic spin fluctuations in electron-doped cobaltate NaxCoO2·yH2ONaxCoO2·yH2O based on the kinetic energy driven superconductivity mechanism. We show that the superconducting state is governed by both charge carrier pairing and quasiparticle coherent, and displays a common dome-shaped phase diagram in agreement with experimental results. By calculating the dynamical spin structure factor, we theoretically find that the magnetic excitation shows a commensurate resonance peak, which locates at antiferromagnetic wave vector Q(2π/3,2π/3) for a broad range of low energies, then evolves outward into six incommensurate magnetic scattering peaks with increasing energy. Such commensurate–incommensurate spin resonance excitation should be measured by the inelastic neutron scattering (INS) technique. Our present results strongly suggest that magnetic resonance can indeed be one of the fundamental features in doped Mott insulators.Highlights► Electron doped Mott insulators on a triangular lattice. ► Fermion–spin theory within the charge–spin separation framework. ► The kinetic energy driven superconductivity mechanism. ► Commensurate–incommensurate spin resonance excitations in superconducting states.

The spin dynamics of electron doped Mott insulators on a triangular lattice is studied based on the t–Jt–J model. It is found that the particularly universal behaviors of integrated dynamical spin structure factor seen in the doped Mott insulators on a square lattice, are absent in the doped Mott insulators on a triangular lattice, indicating the presence of the normal state gap. As a result, the spin–lattice relaxation rate 1/T11/T1 divided by TT reduces with decreasing temperatures in the temperature region above 0.2J≈50K, then follows a Curie–Weiss-like behavior at the temperature less than 50 K, in qualitative agreement with experimental observations.Highlights► A deviation from a universal behavior was shown in temperature dependence of dynamical spin structure factor. ► A weak normal state gap caused by spin frustration was found. ► Spin–lattice relaxation reproduces the experimental observation, and was explained by anomalous spin dynamics.