Structural properties of local integrals of motion across the many-body localization transition via a fast and efficient method for their construction

TL;DR

This paper introduces a fast, non-perturbative method to construct local integrals of motion in disordered quantum systems, revealing their structural changes across the many-body localization transition and linking it to a percolation transition in Hilbert space.

Contribution

The authors develop a novel, efficient approach to construct LIOMs near the MBL transition, enabling detailed structural analysis and revealing a percolation transition in the Hilbert space.

Findings

MBL transition coincides with a percolation transition in Hilbert space.

The new method accurately constructs LIOMs near the transition point.

Finite-size scaling yields critical disorder and correlation exponents.

Abstract

Many-body localization (MBL) is a novel prototype of ergodicity breaking due to the emergence of local integrals of motion (LIOMs) in a disordered interacting quantum system. To better understand the role played by the existence of such macroscopically LIOMs, we explore and study some of their structural properties across the MBL transition. We first, consider a one-dimensional XXZ spin chain in a disordered magnetic field and introduce and implement a non-perturbative, fast, and accurate method of constructing LIOMs. In contrast to already existing methods, our scheme allows obtaining LIOMs not only in the deep MBL phase but rather, near the transition point too. Then, we take the matrix representation of LIOM operators as an adjacency matrix of a directed graph whose elements describe the connectivity of ordered eigenbasis in the Hilbert-space. Our cluster size analysis for this graph shows that the MBL transition coincides with a percolation transition in the Hilbert-space. By performing finite-size scaling, we compare the critical disorder and correlation exponent $\nu$ both in the presence and absence of interaction. Finally, we also discuss how the distribution of diagonal elements of LIOM operators in a typical cluster signals the transition.