Plaquette Valence Bond Theory of High-Temperature Superconductivity

TL;DR

This paper introduces a strong-coupling plaquette valence bond theory for high-temperature superconductivity, highlighting a quantum critical point and explaining the pseudogap via local singlet states within the Hubbard model.

Contribution

It proposes a novel strong-coupling approach based on plaquette singlets and quantum criticality, extending resonating valence bond ideas to high-Tc superconductors.

Findings

Maximum d-wave order parameter at the localization-itinerancy border

Explanation of pseudogap formation via soft-fermion modes

Identification of a quantum critical point in the plaquette

Abstract

We present a strong-coupling approach to the theory of high-temperature superconductivity based on the observation of a quantum critical point in the plaquette within the t,t' Hubbard model. The crossing of ground state energies in the N=2,3,4 sectors occurs for parameters close to the optimal doping. The theory predicts the maximum of the d(x2-y2)-wave order parameter at the border between localized and itinerant electron behavior and gives a natural explanation for the pseudo-gap formation via soft-fermion mode related to local singlet states of the plaquette in the environment. Our approach follows the general line of resonating valence bond theory stressing a crucial role of singlets in the physics of high-Tc superconductors, but focuses on the formation of local singlets, similar to phenomena observed in frustrated one-dimensional quantum spin models.