Density-matrix renormalization group study of pairing when electron-electron and electron-phonon interactions coexist: effect of the electronic band structure

摘要

Density-matrix renormalization group is used to study the pairing when bothof electron-electron and electron-phonon interactions are strong in theHolstein-Hubbard model at half-filling in a region intermediate between theadiabatic (Migdal's) and antiadiabatic limits. We have found: (i) the pairingcorrelation obtained for a one-dimensional system is nearly degenerate with theCDW correlation in a region where the phonon-induced attraction is comparablewith the electron-electron repulsion, but (ii) pairing becomes dominant when wedestroy the electron-hole symmetry in a trestle lattice. This provides aninstance in which pairing can arise, in a lattice-structure dependent manner,from coexisting electron-electron and electron-phonon interactions.