Band-structure effects in the Hubbard chain

We present results of quantum Monte Carlo simulations for the one-dimensional Hubbard model with next-nearest-neighbour hopping (t(2)). The appearance of double peaks in the spin and charge structure factors is identified with the doubling of ground states, each with its corresponding excitation modes. A quantitative phase diagram in the t(2)-rho (density) plane for fixed on-site coupling is obtained, and compared with weak-coupling renormalization group predictions. Four regions in this phase diagram are clearly identified: (i) singly peaked charge and spin structure factors; (ii) singly peaked ferromagnetic and charge fluctuations; (iii) singly peaked charge fluctuations and doubly peaked spin fluctuations; and (iv) doubly peaked spin and charge fluctuations.