Bipolaron superconductivity in double-bilayer moiré-Hubbard TMDs

Spin-polarons are bound states of a hole and one or more spin-flips in a spin-polarized background. Even though such states incur a magnetic energy cost, they can still be energetically favorable compared to bare hole excitations in frustrated lattices with weak ferromagnetic order, primarily due to the minimization of the hole's kinetic energy. This phenomenon is notably observed in moiré-Hubbard transition metal dichalcogenide (TMD) bilayers, such as MoTe₂/WSe₂. In this study, we consider two stacked copies of a moiré-Hubbard TMD bilayer connected via tunnel coupling. Utilizing a combination of continuum models and Density Matrix Renormalization Group (DMRG) computations, we identify a parameter region where layer-antiferromagnet (LAF) order is stabilized due to interlayer superexchange interactions. We demonstrate that, across a broad range of experimentally realistic parameters, the system's lowest energy charged excitations are charge 2e bipolarons, which are bound states of spin-polarons across the two layers. We investigate the resulting superconductivity emerging from bipolaron condensation and discuss the experimental parameters under which such superconductors are likely to emerge. Additionally, we examine the competition with larger spin-polarons and the stability of the system against different perturbations.