Quantum Monte Carlo and exact diagonalization study of a dynamic Hubbard model

摘要

A one-dimensional model of electrons locally coupled to spin-1/2 degrees offreedom is studied by numerical techniques. The model is one in the class of$dynamic$ $Hubbard$ $models$ that describe the relaxation of an atomic orbitalupon double electron occupancy due to electron-electron interactions. We studythe parameter regime where pairing occurs in this model by exactdiagonalization of small clusters. World line quantum Monte Carlo simulationssupport the results of exact diagonalization for larger systems and show thatkinetic energy is lowered when pairing occurs. The qualitative physics of thismodel and others in its class, obtained through approximate analyticcalculations, is that superconductivity occurs through hole undressing even inparameter regimes where the effective on-site interaction is stronglyrepulsive. Our numerical results confirm the expected qualitative behavior, andshow that pairing will occur in a substantially larger parameter regime thanpredicted by the approximate low energy effective Hamiltonian.