DMRG-based downfolding of the three-band Hubbard model

We study the three-band Hubbard model using a DMRG-based downfolding method. The resulting single-band model includes important terms which have been overlooked. These two-site occupancy-dependent hopping terms appear to be important in capturing the pairing in a single-band model for hole-doped cuprates. A mean field treatment of the new terms is not nearly as effective in increasing pairing as the terms themselves, as revealed by a measurement of the superconducting phase stiffness.

The procedure of downfolding is as follows: we simulate the three-band Hubbard model and obtain the ground state wavefunction; by identifying the natural orbitals, we truncate the degrees of freedom to a single band and construct the appropriate Wannier functions; a downfolded single-band model is generated by projecting the three-band Hamiltonian to the basis of the Wannier functions. The accuracy of the downfolding is determined by the occupancy of the natural orbitals omitted; we find this occupancy is quite small (<2%), so downfolding to a single band should be accurate.