Defect-mediated pairing and dissociation of strongly correlated electrons in low-dimensional lattices

We study the quantum dynamics of a strongly correlated electron pair in a one-dimensional lattice, focusing on the occurrence of local dissociation/pairing mechanisms induced by a site energy defect. To this end, we simulate the time evolution of two interacting electrons on a finite-size chain governed by an extended Hubbard Hamiltonian including on-site Coulomb repulsion $U$ and nearest-neighbor interaction $V$, along with single-electron hopping $J$. By introducing a local site energy defect with amplitude $\mathrm{\ensuremath{\Delta}}$, we show that a transition between spatially paired/dissociated electrons can occur in the vicinity of this site. Such mechanisms arise in a strongly correlated regime with nonzero nearest-neighbor Coulomb interactions and under the conditions $(U\ensuremath{\sim}V\ensuremath{\sim}\mathrm{\ensuremath{\Delta}})\ensuremath{\gg}J$. To rationalize these phenomena, we reformulate the two-electron dynamics of the original Hubbard chain as an effective single-particle problem on a two-dimensional network. Within this framework, we show that the pairing/dissociation dynamics are driven by resonances between two distinct families of two-electron eigenstates: (i) states with two spatially well-separated electrons with one located at the site defect, and (ii) states with a locally bound electron located away from the defect. At resonance, these states hybridize, allowing transitions from locally paired to dissociated electrons---and vice versa---in the vicinity of the defect. These results provide further insights into exotic pairing phenomena in strongly correlated electronic systems and may have implications for the design of tunable many-body states in low-dimensional quantum materials.