Correlations in a two--chain Hubbard model

TL;DR

This paper investigates the correlation functions in a two-chain Hubbard model using a numerical approach, revealing a gapped spin-liquid state at half-filling and power-law decay of pair correlations below half-filling.

Contribution

It provides detailed numerical analysis of spin and pair correlations in a two-chain Hubbard model, highlighting the nature of the ground state and correlation decay behaviors.

Findings

Exponential decay of correlations at half-filling indicating a gapped spin-liquid.

Incommensurate antiferromagnetic correlations below half-filling.

Power-law decay of pair correlations similar to non-interacting case.

Abstract

Equal time spin--spin and pair field correlation functions are calculated for a two-chain Hubbard model using a density-matrix numerical renormalization group approach. At half-filling, the antiferromagnetic and pair field correlations both decay exponentially with the pair field having a much shorter correlation length. This is consistent with a gapped spin-liquid ground state. Below half--filling, the antiferromagnetic correlations become incommensurate and the spin gap persists. The pair field correlations appear to follow a power law decay which is similar to their non-interacting U=0 behavior.