Superconductivity and trimers on attractive-$U$ Hubbard ladders

Abstract: We investigate the interplay between superconducting correlations and trimer formation in polarized two-component Fermi gases confined to multileg attractive-$U$ Hubbard ladders. Employing density matrix renormalization group (DMRG) simulations, we explore the effects of spin-dependent tunneling amplitudes on these systems. Specifically, we analyze how bound states of three fermions (trimers) impact Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting correlations at commensurate charge carrier densities, where $2n_{\uparrow} = n_{\downarrow}$. In one-dimensional (1D) systems, trimer formation is known to suppress FFLO correlations exponentially. Our results demonstrate that this suppression persists on ladder lattices of small width, effectively mirroring the 1D behavior. However, we find a striking departure from the 1D regime as the ladder width increases. On ladders with a width of four legs, the influence of trimers on superconducting correlations becomes negligible, suggesting that wider ladder systems provide a distinct environment where FFLO-like pairing remains robust even in the presence of trimer states. These findings underscore the dimensional crossover in Hubbard systems and shed light on the mechanisms governing superconductivity and bound-state formation in strongly correlated fermionic systems. Our work has implications for understanding unconventional superconductivity in strongly correlated systems.