Neel Order and Electron Spectral Functions in the Two-Dimensional Hubbard Model: a Spin-Charge Rotating Frame Approach

TL;DR

This paper develops a spin-charge rotating frame approach to analyze the spectral functions in the 2D Hubbard model, revealing how electrons decay into separate spin and charge excitations in the antiferromagnetic state.

Contribution

It introduces a self-consistent SU(2)xU(1) rotor method to compute spectral functions, explicitly incorporating spin-charge separation and gauge fields in the Hubbard model.

Findings

Emergence of a sharp peak indicating electron decay into spin and charge excitations.

Spectral functions derived from convolution of spin, charge, and pseudo-fermion Green's functions.

Applicable to any Coulomb interaction strength in the Hubbard model.

Abstract

Using recently developed quantum SU(2)xU(1) rotor approach, that provides a self-consistent treatment of the antiferromagnetic state we have performed electronic spectral function calculations for the Hubbard model on the square lattice. The collective variables for charge and spin are isolated in the form of the space-time fluctuating U(1) phase field and rotating spin quantization axis governed by the SU(2) symmetry, respectively. As a result interacting electrons appear as composite objects consisting of bare fermions with attached U(1) and SU(2) gauge fields. This allows us to write the fermion Green's function in the space-time domain as the product CP^1 propagator resulting from the SU(2) gauge fields, U(1) phase propagator and the pseudo-fermion correlation function. As a result the problem of calculating the spectral line shapes now becomes one of performing the convolution of spin, charge and pseudo-fermion Green's functions. The collective spin and charge fluctuations are governed by the effective actions that are derived from the Hubbard model for any value of the Coulomb interaction. The emergence of a sharp peak in the electron spectral function in the antiferromagnetic state indicates the decay of the electron into separate spin and charge carrying particle excitations.