Beyond Topological Invariants: Order Parameters from Dominant Fock-state Patterns

TL;DR

This paper proposes a novel real-space order parameter scheme based on dominant Fock states to classify phases in many-body quantum systems, revealing hidden structures beyond topological invariants.

Contribution

It introduces a general method for constructing order parameters from Fock state patterns, providing refined phase classification and robustness in disordered and transition systems.

Findings

Revealed hidden sub-structures in topological phases using new OPs.

Demonstrated the method's effectiveness in the extended SSH model.

Provided a finite-size diagnostic for the BKT transition in XXZ model.

Abstract

We introduce a general scheme for constructing order parameters (OPs) by extracting generic patterns from the dominant Fock states of many-body ground states. While topological phases are traditionally characterized by non-local invariants, we demonstrate that our real-space OPs provide a more refined classification. In the extended Su-Schrieffer-Heeger model, we show that the standard winding number is insufficient to fully distinguish all phases; our OPs reveal a hidden sub-structure where each topological sector splits into two distinct phases. Beyond identifying the phase boundaries, these OPs quantify the depth of a phase, and remain robust in characterizing transitions in disordered systems. Furthermore, our approach provides a practical finite-size diagnostic for the Berezinskii-Kosterlitz-Thouless transition in the interacting spin-1/2 XXZ model. The presented framework offers a broadly applicable tool for uncovering the phase diagrams of diverse interacting and non-interacting quantum many-body systems.