Electron pairing in one-dimensional quasicrystals

Electron pairing in one-dimensional binary Hubbard chains is studied for different values of the band-filling using the density matrix renormalization group method. The systems consist of linear arrays of sites with two types of on-site correlations defined by two potentials: UAUA being attractive (<0), and UBUB repulsive (>0). The atomic levels of the system are modulated with periodic and quasiperiodic ordering, in the latter case following the Fibonacci sequence. We analyze the effect of such modulations and calculate the electron pairing phase diagram as a function of the band-filling. It is observed that there is a critical value of the band-filling where the behavior of the periodic and the Fibonacci binary Hubbard chains is reversed.