Quantum Avalanches in $\mathbb{Z}_2$-preserving Interacting Ising Majorana Chain

TL;DR

This paper investigates the instability of many-body localized phases in a disordered quantum Ising Majorana chain, revealing how avalanche mechanisms and finite-size effects influence phase stability and thermalization.

Contribution

It introduces a detailed analysis of avalanche effects and finite-size scaling in a complex $ ext{Z}_2$-preserving interacting Ising Majorana chain, highlighting the instability of MBL phases.

Findings

MBL phases are unstable at finite sizes due to avalanche effects.

Critical disorder strength drifts with system size, affecting phase stability.

Both MBL paramagnetic and spin-glass phases are unstable in finite systems.

Abstract

Recent numerical works have revealed the instability of many-body localized (MBL) phase in disordered quantum many-body systems with finite system sizes and over finite timescales. This instability arises from Griffith regions that occur at the thermodynamic limit, which rapidly thermalize and affect the surrounding typical MBL regions, introducing an avalanche mechanism into the system. Here, we consider the $\mathbb{Z}_2$-preserving interacting Ising Majorana chain model, which exhibits a more complex phase diagram, where an ergodic phase emerges between two MBL phases with different long-range order properties. We calculate the dynamic characteristics of the model when coupled to an infinite bath under perturbation, and through scaling behavior of the slowest thermalization rate, we find how critical disorder strengths in finite-size systems are affected by the avalanche mechanism. We also employe the embedded inclusion model and use the time evolution of mutual information between each spin and the artificial Griffith region to probe the diffusion of the thermal bubble. We observe that in finite-sized systems, the critical disorder strength gradually drifts away from the central. Our work demonstrate that both MBL paramagnetic phase and MBL spin-glass phase are unstable at finite sizes.