Diagrama de fases e emaranhamento em sistemas de spins Ising-Hubbard

Abstract

Over the last decades, several works have been devoted to the investigation of a new class of hybrid spin systems. In this thesis the degree of fermionic entanglement is examined in an exactly solvable Ising-Hubbard ladder, which involves interacting electrons on the ladders rungs described by Hubbard dimers at half-filling on each rung, accounting for intrarung hopping and Coulomb terms. The coupling between neighboring Hubbard dimers is assumed to have an Ising-like nature. The ground-state phase diagram consists of four distinct regions corresponding to the saturated paramagnetic, the classical antiferromagnetic, the quantum antiferromagnetic, and a mixed classical-quantum phase. We have exactly computed the fermionic concurrence, which measures the degree of quantum entanglement between the pair of electrons on the ladder rungs. The effects of the hopping amplitude, the Coulomb term, temperature, and magnetic fields on the fermionic entanglement are explored in detail. It is shown that the fermionic concurrence displays a reentrant behavior when quantum entanglement is being generated at moderate temperatures above the classical saturated paramagnetic ground state. We also study the ground-state properties of an Ising-Hubbard triangular tube which presents a phase-diagram with up to 6 distinct phases.