Although the single-band Hubbard model for a half-filled square lattice is considered to be an antiferromagnetic (AF) insulator, it is a current vital question to ask what happens if the second nearest-neighbor hopping (t′) is introduced to it. To study this problem, we use the fluctuation exchange (FLEX) approximation together with the variational Monte Carlo (VMC) method. We have obtained basically consistent results: A first-order Mott transition takes place at the Coulomb repulsion U = Uc for a wide range of t′, and robust d-wave SC whose transition temperature is more than 0.01t (t is the nearest-neighbor hopping) appears near the AF and the Mott insulator region. We have also found that the superconductivity as well as an AF long-range order is suppressed as t′ increases, because the AF spin fluctuation becomes weaker.
- Hubbard model
- Spin frustration
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering