Coexistence of antiferromagnetism and unconventional superconductivity in the quasi one-dimensional flat-band system：Creutz lattice

Abstract

Abstract We study the coexistence of antiferromagnetism and unconventional superconductivity on the Creutz lattice which shows strictly flat bands in the noninteracting regime. The famous renormalized mean-field theory is used to deal with strongly electron-electron repulsive Hubbard interaction per- formed by the effective low energy t-J model, the superfluid weight of the unconventional superconducting state has been calculated via the linear response theory. An unconventional superconducting state with both spin-singlet and staggered spin-triplet pairs emerges beyond a critical antiferromagnetic coupling interaction, meanwhile, antiferromagnetism accompanies this state. The superconducting state with only spin-singlet pairs is dominant with paramagnetic. A phase is analogous to the pseudogap phase which shows electrons go to preformed pairs but does not cause supercurrent has been present. We also show the superfluid behavior of an unconventional superconducting state and its critical temperature. It is proved directly that the flat band can effectively raise the critical temperature of superconductivity. It is implementable to simulate and control strongly correlated electrons’ behavior on the Creutz lattice in the ultracold atoms experiment or other artificial structures. Our results may help the understanding of the interplay between unconventional superconductivity and magnetism.