Nontrivial quantized Berry phases for itinerant spin liquids

TL;DR

This paper investigates quantized Berry phases as local order parameters in t-J models, revealing topologically stable textures and nontrivial phases associated with itinerant singlets, especially in large J/t regimes.

Contribution

It introduces a novel application of non-Abelian Berry phases as local order parameters in t-J models, demonstrating their topological stability and relation to itinerant singlets.

Findings

Local Berry phases are quantized and topologically stable.

Itinerant singlets carry a Berry phase of pi.

In 1D t-J models, Berry phases are uniformly pi for N=4n+2 electrons.

Abstract

Quantized Berry phases as local order parameters in t-J models are studied. A texture pattern of the local order parameters is topologically stable due to the quantization of non-Abelian Berry phases defined by low-energy states below a spin gap, which exists in the large J/t case with a few electrons. We have confirmed that itinerant singlets in the wide class of t-J models carry the nontrivial Berry phase pi. In the large J/t case for the one-dimensional t-J model, Berry phases are uniformly pi when the number of electrons is N =4n +2, ($n=0,1,2,...$).