title: Entanglement entropy beyond the free case.
abstract: We present a perturbative method to compute the ground state entanglement entropy for interacting systems. We apply it to a collective model of mutually interacting spins in a magnetic field. At the quantum critical point, the entanglement entropy scales logarithmically with the subsystem size, the system size, and the anisotropy parameter. We determine the corresponding scaling prefactors and evaluate the leading finite-size correction to the entropy. Our analytical predictions are in perfect agreement with numerical results.
authors.affiliation: Institute for Theoretical Physics C, RWTH Aachen, 52056 Aachen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Barthel
authors.forename: Sébastien
authors.initials: S
authors.lastname: Dusuel
authors.forename: Julien
authors.initials: J
authors.lastname: Vidal