Band flattening has been identified as a key ingredient to correlation phenomena in Moiré materials and beyond. Here, we examine strongly repulsive fermions on a ladder—a minimal platform for unconventional $d$-wave pairing—and show that flattening of the lower band through an additional diagonal hopping term produces non-Fermi-liquid behavior, evidenced by the violation of Luttinger's theorem, as well as axial $d$-wave pairing correlations. Alternatively, a plaquette ring exchange can also generate pairing, albeit with a distinct diagonal $d$-wave pairing symmetry. Hence, our finding showcases a competition of different unconventional pairing channels, and demonstrates via a simple model how band geometry can induce fermionic pairing. This offers broadly relevant insights for correlated flat-band systems, ranging from ultracold atoms to strongly interacting electrons in solids.

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• Luttinger's theorem
• Pairing mechanisms
• d-wave
• 1-dimensional systems
• Strongly correlated systems
• Density matrix renormalization group
• Extended Hubbard model