Incommmensurability and unconventional superconductor to insulator transition in the hubbard model with bond-charge interaction

Phys Rev Lett. 2007 Nov 16;99(20):206401. doi: 10.1103/PhysRevLett.99.206401. Epub 2007 Nov 13.

Abstract

We determine the quantum phase diagram of the one-dimensional Hubbard model with bond-charge interaction X in addition to the usual Coulomb repulsion U>0 at half-filling. For large enough X<t the model shows three phases. For large U the system is in the spin-density wave phase as in the usual Hubbard model. As U decreases, there is first a spin transition to a spontaneously dimerized bond-ordered wave phase and then a charge transition to a novel phase in which the dominant correlations at large distances correspond to an incommensurate singlet superconductor.