Band and Mott Insulators and Superconductivity in Honeycomb-Lattice Ionic-Hubbard Model

TL;DR

This study investigates superconductivity in a honeycomb-lattice ionic-Hubbard model, revealing that weak doping of a band insulator can induce a spin-singlet d-wave superconducting state driven by spin fluctuations.

Contribution

It introduces a variational Monte Carlo analysis of the ionic-Hubbard model on a honeycomb lattice, highlighting the emergence of d-wave superconductivity in doped band insulators.

Findings

Spin fluctuation persists in weakly doped band insulators.

Spin-singlet d-wave superconductivity is realized upon doping.

Results support unconventional superconductivity in layered nitrides.

Abstract

Motivated by superconductivity (SC) in layered nitrides, we study an ionic-Hubbard model on a honeycomb lattice, which consists of two sublattices with an energy-level offset, by using an optimization variational Monte Carlo method. Parameter values for the Coulomb interaction and the energy-level offset, to realize a band insulator in non-doped state, are evaluated, and the SC state is investigated in a carrier-doped band insulator. It is found that, in a weakly doped band insulator, spin fluctuation remains and the spin-singlet d-wave SC state is realized. Present results support an unconventional spin-singlet SC state suggested by the experimental observations in layered nitrides.