Superconductivity in the bilayer Hubbard model: Are two Fermi surfaces better than one?

Abstract

Fully occupied or unoccupied bands in a solid are often considered inert and irrelevant to a material's low-energy properties. But the discovery of enhanced superconductivity in heavily electron-doped FeSe-derived superconductors poses questions about the possible role of incipient bands (those laying close to but not crossing the Fermi level) in pairing. To answer this question, researchers have studied pairing correlations in the bilayer Hubbard model, which has an incipient band for large interlayer hopping t ⊥ , using many-body perturbation theory and variational methods. They have generally found that superconductivity is enhanced as one of the bands approaches the Liftshiz transition and even when it becomes incipient. Here, we address this question using the nonperturbative quantum Monte Carlo (QMC) dynamical cluster approximation (DCA) to study the bilayer Hubbard model's pairing correlations. We find that the model has robust s± pairing correlations in the large t ⊥ limit, which can become stronger as one band is made incipient. While this behavior is linked to changes in the effective interaction, we further find that it is counteracted by a suppression of the intrinsic pair-field susceptibility and does not translate to an increased Tc.Our results demonstrate that the highest achievable transition temperatures in the bilayer Hubbard model occur when the system has two bands crossing the Fermi level.

Characterizing the superconducting instability in a two-orbital $d$-$s$ model: insights to infinite-layer nickelate superconductors

“…Specifically, there might exist a 2Dto-3D superconducting states crossover possibly due to the coupling between NiO 2 plane and rareearth spacer layer. This similarity with the ironbased superconductor with nodeless multiband SC is reminiscent of the various studies on the bilayer Hubbard model at strong inter-layer hybridization, where the nodeless s ± -wave pairing is appreciated [71][72][73] .…”

Bilayer Hubbard model: Analysis based on the fermionic sign problem

“…More recently, large scale ground-state QMC calculations [15] have clarified the absence of metallicity at finite values of the interactions, as initially suggested to occur [13,[16][17][18][19], and further corroborated the existence of a magnetic transition in the 3D Heisenberg universality class as the interplane hybridization was increased, similar to that of the bilayer Heisenberg model [20]. Dynamical cluster approximation calculations have also examined the possibility of the enhancement of superconductivity as one of the bands approaches the Lifshitz transition, and its implications for heavily electron-doped FeSe-derived superconductors [21].…”