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

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.

REVTEX 4, 10 pages, 9 figures; submitted to PRB