Pseudogap Phase: Exchange Energy Driven vs. Kinetic Energy Driven

TL;DR

This paper compares two theoretical models of the pseudogap phase in cuprates, showing that one is driven by superexchange energy and the other by kinetic energy, with experimental data favoring the kinetic-energy-driven scenario.

Contribution

It provides a comparative analysis of two mean-field theories of the pseudogap phase based on the t-J model, highlighting their different energy mechanisms and consistency with experiments.

Findings

Pseudogap phase is superexchange-energy-driven in slave-boson RVB state.

Pseudogap phase is kinetic-energy-driven in bosonic RVB state.

Experimental data suggests the pseudogap phase in cuprates is kinetic-energy-driven.

Abstract

We show that both kinetic and superexchange energies of the t-J model may be read off from the optical data, based on an optical sum rule for the Hubbard model. Then we comparatively study two mean-field theories of pseudogap phase based on the t-J model. We find that while the pseudogap phase is superexchange-energy-driven in the slave-boson resonating-valence-bond (RVB) state, it is kinetic-energy-driven in the bosonic RVB state. The sharp contrast in the mechanisms of the pseudogap phases can be attributed to the fact that the antiferromagnetic (AF) correlations behave quite differently in two mean-field states, which in turn distinctly influence the kinetic energy of charge carriers. We elaborate this based on some detailed studies of the superexchange energy, kinetic energy, uniform spin susceptibility, equal-time spin correlations, dynamic spin susceptibility, as well as the optical conductivity. The results provide a consistent picture and understanding on two physically opposite origins of pseudogap phase. In comparison with experimental measurements, we are led to conclude that the pseudogap phase in the cuprates should be kinetic-energy-driven in nature.