Evolution of Electronic Spectral Weight in the Hubbard ladder

Although the number of electronic bands is usually considered invariant in a conventional band picture, the electronic states can generally emerge, grow, and disappear as the electron density changes in strongly correlated systems. Here, the evolution of the electronic states as a function of the electron density is illustrated in the Hubbard ladder in the strong Coulomb repulsion and strong intra-rung hopping regime using the non-Abelian dynamical density-matrix renormalization group method and perturbation theory. An emergent mode in the low-electron density regime grows with the electron density and plays a significant role in the dimer Mott physics at quarter filling, whereas an originally non-interacting band at zero electron density loses the spectral weight and disappears in the Mott transition at half filling, which leads to the spin excitation of the Mott insulator. The emergence and disappearance of electronic states, which have almost been overlooked in conventional band theory and Fermi liquid theory, are particularly important in understanding of the physics around the Mott transition.