Frustration-induced incommensurate solids in the extended Bose-Hubbard model

The extended Bose-Hubbard model with nearest-neighbor and next-nearest-neighbor repulsive interactions on a square lattice is investigated by using the quantum Monte Carlo method. We find that for the cases of weak next-nearest-neighbor interactions and small hoppings, incommensurate solids of fractional densities varying from 1/4 to 1/2 can be stabilized in the thermodynamic limit. We further show that the continuous changes of ordering wave vectors from (π,π/2) [or (π/2,π)] to (π,π) within the incommensurate solid phase can be understood by the mechanism of domain wall formation. The related ground-state phase diagram and thermal phase transitions are also discussed.