Universality classes of order parameters composed of many body bound states

TL;DR

This paper explores theoretical models where conduction electrons and localized spins form composite order parameters, revealing a connection to spin liquids with fractionalized excitations that are robust against local perturbations.

Contribution

It introduces a detailed theoretical framework for composite order in electron-spin systems, emphasizing the robustness and symmetry properties of resulting spin liquid states.

Findings

Composite order relates to spin liquids with fractionalized excitations.

Spin liquids involve both conduction and localized electron spins.

Robustness of spin liquid states against local symmetry-preserving perturbations.

Abstract

This theoretical paper discusses microscopic models giving rise to special types of order in which conduction electrons are bound together with localized spins to create composite order parameters. It is shown that composite order is related to the formation of a spin liquid with gapped excitations carrying quantum numbers which are a fraction of those of electron. These spin liquids are special in the sense that their formation necessarily involves spin degrees of freedom of both the conduction and the localized electrons. A detailed description of such spin liquid states is presented with a special emphasize on a demonstration of their robustness against local perturbations preserving the Lie group symmetry and the translational invariance.