Pair Correlations in Doped Hubbard Ladders

TL;DR

This paper uses advanced numerical simulations to investigate the dominant correlations in doped Hubbard ladders, confirming that superconducting correlations prevail at very low doping levels.

Contribution

It provides improved estimates of correlation functions and Luttinger parameters using larger system sizes and higher accuracy density matrix renormalization group simulations.

Findings

Superconducting correlations dominate at very low doping.

Enhanced simulation techniques yield more accurate long-distance correlation estimates.

Results support analytical predictions about superconductivity in doped Hubbard ladders.

Abstract

Hubbard ladders are an important stepping stone to the physics of the two-dimensional Hubbard model. While many of their properties are accessible to numerical and analytical techniques, the question of whether weakly hole-doped Hubbard ladders are dominated by superconducting or charge-density-wave correlations has so far eluded a definitive answer. In particular, previous numerical simulations of Hubbard ladders have seen a much faster decay of superconducting correlations than expected based on analytical arguments. We revisit this question using a state-of-the-art implementation of the density matrix renormalization group algorithm that allows us to simulate larger system sizes with higher accuracy than before. Performing careful extrapolations of the results, we obtain improved estimates for the Luttinger liquid parameter and the correlation functions at long distances. Our results confirm that, as suggested by analytical considerations, superconducting correlations become dominant in the limit of very small doping.