Ferromagnetic spin correlations in the two-dimensional Hubbard model

TL;DR

This paper investigates spin correlations in the 2D Hubbard model using cluster approximations, revealing enhanced ferromagnetic correlations linked to composite spin-1 moments and their relation to pseudogap phenomena and unconventional superconductivity.

Contribution

It provides new insights into ferromagnetic spin correlations and their connection to spin-freezing and pseudogap behavior in the 2D Hubbard model.

Findings

Enhanced ferromagnetic correlations on lattice diagonals.

Correlation emergence coincides with pseudogap temperature T*.

Results support spin-freezing theory of unconventional superconductivity.

Abstract

We analyze the dynamical nearest-neighbor and next-nearest-neighbor spin correlations in the 4-site and 8-site dynamical cluster approximation to the two-dimensional Hubbard model. Focusing on the robustness of these correlations at long imaginary times, we reveal enhanced ferromagnetic correlations on the lattice diagonal, consistent with the emergence of composite spin-1 moments at a temperature scale that essentially coincides with the pseudo-gap temperature $T^*$. We discuss these results in the context of the spin-freezing theory of unconventional superconductivity.