Magnetism and Pairing in Hubbard Bilayers.

TL;DR

This study uses Quantum Monte Carlo simulations to explore magnetic and pairing behaviors in a Hubbard bilayer model, revealing dominant inter-plane pairing with potential implications for high-temperature superconductivity.

Contribution

It demonstrates that inter-plane pairing with d_{x^2-z^2} symmetry dominates in Hubbard bilayers, highlighting a possible pairing mechanism relevant to cuprate superconductors.

Findings

Inter-plane pairing with d_{x^2-z^2} symmetry is dominant.

Pair formation occurs via antiferromagnetic correlations at large t_z.

Pairing is associated with the spin gap crossover temperature.

Abstract

We study the Hubbard model on a bilayer with repulsive on-site interactions, $U$, in which fermions undergo both intra-plane ($t$) and inter-plane ($t_z$) hopping. This situation is what one would expect in high-temperature superconductors such as YBCO, with two adjacent CuO$_2$ planes. Magnetic and pairing properties of the system are investigated through Quantum Monte Carlo simulations for both half- and quarter-filled bands. We find that in all cases inter-planar pairing with $d_{x^2-z^2}$ symmetry is dominant over planar pairing with $d_{x^2-y^2}$ symmetry, and that for $t_z$ large enough pair formation is possible through antiferromagnetic correlations. However, another mechanism is needed to make these pairs condense into a superconducting state at lower temperatures. We identify the temperature for pair formation with the spin gap crossover temperature. [Submitted to Phys. Rev. B]