Infra-red expansion of entanglement entropy in the Interacting Resonant Level Model

TL;DR

This paper introduces a perturbative method to compute entanglement entropy in the Interacting Resonant Level Model at low energies, revealing universal behaviors and interaction-dependent effects in the strong coupling regime.

Contribution

It develops an exact quantization scheme for Renyi entropies in the IRLM using integrability and conformal field theory techniques, applicable at arbitrary order in $1/T_B$.

Findings

Universal quantities are well approximated by free fermion results for attractive interactions.

Strong interaction dependence is observed for repulsive Coulomb interactions.

The method allows for precise entanglement entropy calculations at finite system size and temperature.

Abstract

In this paper we develop a method to describe perturbatively the entanglement entropy in a simple impurity model, the interacting resonant level model (IRLM), at low energy (i.e. in the strong coupling regime). We use integrability results or the Kondo model to describe the infra-red fixed point, conformal field theory techniques initially developped by Cardy and Calabrese and a quantization scheme that allows one to compute exactly Renyi entropies at arbitrary order in $1/T_B$ in principle, even when the system size or the temperature is finite. We show that those universal quantities at arbitrary interaction parameter in the strong coupling regime are very well approximated by the same quantities in the free fermion system in the case of attractive Coulomb interaction, whereas a strong dependence on the interaction appears in the case of repulsive interaction.