Confinement-induced enhancement of superconductivity in a spin-21 fermion chain coupled to a Z2 lattice gauge field

We investigate a spin -1/2 fermion chain minimally coupled to a Z2 gauge field. In the sector of the gauge generator (G) over cap (j) = -1, the model reduces to the Hubbard model with repulsive on-site interaction coupled to a Z2 gauge field. We uncover how electric fields affect low-energy excitations by both analytical and numerical methods. In the half-filling case, despite electric fields, the system is still a Mott insulator, just like the Hubbard model. For hole-doped systems, holes are confined under nonzero electric fields, resulting in a hole-pair bound state. Furthermore, this bound state also significantly affects the superconductivity, which manifests itself in the emergence of attractive interactions between bond-singlet Cooper pairs. Specifically, numerical results reveal that the dimension of the dominant superconducting order parameter becomes smaller when increasing the electric field, signaling an enhancement of the superconducting instability induced by lattice fermion confinement. The superconducting order can even be the dominant order of the system for suitable doping and large applied electric field. The confinement also induces a pi momentum for the dominant superconducting order parameter leading to a quasi-long-range pair density wave order. Our results provide insights for understanding unconventional superconductivity in Z2 lattice gauge theories and might be experimentally addressed in quantum simulators.

Automated summary

We study a spin-1/2 fermion chain coupled to a Z2 gauge field and analyze the effects of electric fields on low-energy excitations. In the half-filling case, the system remains a Mott insulator despite the presence of electric fields. For hole-doped systems, holes are confined under nonzero electric fields, leading to the formation of hole-pair bound states. These bound states significantly influence superconductivity, demonstrating the emergence of attractive interactions between bond-singlet Cooper pairs. Furthermore, lattice fermion confinement induced by electric fields enhances the superconducting instability. Our findings provide insights into unconventional superconductivity in Z2 lattice gauge theories and have implications for experimental investigation in quantum simulators.