Anomalous behaviors of the charge and spin degrees of freedom in the CuO double chains of PrBa$_2$Cu$_4$O$_8$

TL;DR

This study uses the density-matrix renormalization-group method to explore the electronic states of a two-chain Hubbard model for CuO double chains in PrBa2Cu4O8, revealing charge orderings and a potential metallic state with a small spin gap.

Contribution

It demonstrates the presence of charge-ordered phases and a broad metallic region in the model, providing insights into the low-energy electronic state of the material.

Findings

Charge-ordered stripe and in-line patterns identified.

A wide region with vanishing charge gap suggests metallic or Tomonaga-Luttinger liquid behavior.

The material likely exhibits a metallic state with a small spin gap.

Abstract

The density-matrix renormalization-group method is used to study the electronic states of a two-chain Hubbard model for CuO double chains of PrBa$_2$Cu$_4$O$_8$. We show that the model at quarter filling has the charge ordered phases with stripe-type and in-line--type patterns in the parameter space, and in-between, there appears a wide region of vanishing charge gap; the latter phase is characteristic of either Tomonaga-Luttinger liquid or a metallic state with a spin gap. We argue that the low-energy electronic state of the CuO double chains of PrBa$_2$Cu$_4$O$_8$ should be in the metallic state with a possibly small spin gap.