# Many-body entanglement in a topological chiral ladder

## TL;DR

This paper investigates many-body entanglement signatures of topological phase transitions in a chiral ladder, revealing sharp changes in entanglement entropy and concurrence that characterize the transition.

## Contribution

It provides a detailed analysis of entanglement entropy and concurrence as indicators of topological phase transitions in a chiral ladder system, highlighting new microscopic insights.

## Key findings

- Entanglement entropy shows a sharp signature at the transition point.
- Change in entanglement entropy when adding/removing a particle is exactly -log(2) in trivial phase.
- Derivative of average concurrence peaks sharply at the transition.

## Abstract

We find that the topological phase transition in a chiral ladder is characterized by dramatic signatures in many body entanglement entropy between the legs, close to half-filling. The value of entanglement entropy for various fillings close to half-filling is identical, at the critical point, but splays out on either side, thus showing a sharp signature at the transition point. A second signature is provided by the change in entanglement entropy when a particle is added (or subtracted) from half-filling which turns out to be exactly $-\log{2}$ in the trivial phase, but zero in the topological phase. A microscopic understanding of tendencies to form singlets along the rungs in the trivial phase, and along the diagonals in the topological phase, is afforded by a study of concurrence. At the topological phase transition the magnitude of the derivative of the average concurrence of all the rungs shows a sharp peak. Also, at the critical point, the average concurrence is the same for various fillings close to half-filling, but splays out on either side, just like entanglement entropy.