Effect of Rashba spin-orbit coupling and next-nearest-neighbor hopping on superconductivity in the square-octagon lattice
Phys. Rev. B 113, 104512 – Published 16 March, 2026
DOI: https://doi.org/10.1103/f7rt-5vwb
Abstract
Recent studies have highlighted the role of flat bands and Van Hove singularities in enhancing electronic correlations, which can influence unconventional superconductivity. Here, we present a computational study of a two-dimensional superconductor on the square-octagon lattice, a geometry characterized by multiple flat bands, Van Hove singularities, and magnetic-flux tunable band dispersion. Using the Bogoliubov–de Gennes formalism, we investigate the effects of next-nearest-neighbor (NNN) hopping and Rashba spin-orbit coupling (SOC) on the superconducting state. We compute superconducting phase diagrams, emphasizing the impact of a high density of states on the order parameter, and examine the robustness of the two superconducting domes previously reported under variations in NNN hopping and SOC. We further evaluate the superfluid stiffness and study the Rashba SOC induced spin-triplet pairing correlations coexisting in the presence of the singlet order. Additionally, for weak attractive interactions, we demonstrate the enhancement of the critical temperature by varying the NNN strength, and we analyze how superconductivity evolves with increasing interaction strength. Finally, we revisit the proposal that the two-dome superconducting phase observed in unconventional systems may arise from a single pairing mechanism.
