Abstract
To consider the origin of superconductivity (SC) in layered nitride superconductors, we study an ionic-Hubbard model on a honeycomb lattice, which consists of two sublattices with a level offset, using an optimization variational Monte Carlo method. The parameter values for the Coulomb interaction and the level offset, to realize a band insulator, is evaluated in the non-doped system. In carrier-doped band insulating systems, a spin singlet d-wave SC state is stabilized. The spin fluctuation remains relatively strong even for large level offsets. We find that a renormalization effect of the energy band primarily contributes to the spin fluctuation.
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