Degenerate plaquette physics as key ingredient of high-temperature superconductivity in cuprates

We study the physics of high-temperature cuprate superconductors starting from the highly degenerate four-site plaquette of the t - t' - U Hubbard model as a reference system. The degeneracy causes strong fluctuations when a lattice of plaquettes is constructed. We show that there is a large binding energy between holes when a set of four plaquettes is considered. The next-nearest-neighbour hopping t' plays a crucial role in the formation of these strongly bound electronic bipolarons whose coherence at lower temperature could be the explanation for superconductivity. A complementary approach is cluster dual fermion starting from a single degenerate plaquette, which contains the relevant short-ranged fluctuations from the beginning. It gives d-wave superconductivity as the leading instability under a reasonably broad range of parameters. The origin of the pseudogap is also discussed in terms of the coupling of degenerate plaquettes. Thus, some of the essential elements of cuprate superconductivity appear from the local plaquette physics.

Automated summary

This study investigates the physics of high-temperature cuprate superconductors using the highly degenerate four-site plaquette of the t - t' - U Hubbard model as a reference system. The degeneracy leads to strong fluctuations in a lattice of plaquettes, and it is shown that there is a significant binding energy between holes when considering a set of four plaquettes. The next-nearest-neighbour hopping t' plays a crucial role in the formation of strongly bound electronic bipolarons, which could explain superconductivity at lower temperatures.