Finite-temperature properties of extended Nagaoka ferromagnetism

TL;DR

This study investigates the finite-temperature behavior of an extended Hubbard model with a particle bath, revealing multiple peaks in specific heat and the coexistence of ferromagnetic and antiferromagnetic states influenced by temperature, chemical potential, and interactions.

Contribution

The paper provides a detailed numerical analysis of finite-temperature properties of a Hubbard model with a particle bath, highlighting the microscopic origins of itinerant ferromagnetism.

Findings

Multiple peaks in specific heat indicate various ordering processes.

Magnetic order appears at very low temperatures.

Coexistence and competition of ferromagnetic and antiferromagnetic states depending on parameters.

Abstract

We study finite-temperature properties of a Hubbard model including sites of a particle bath which was proposed as a microscopic model to show itinerant ferromagnetism at finite electron density. We use direct numerical methods, such as exact diagonalization and random vector methods. The temperature dependence of quantities is surveyed in the full range of the temperature. We find that the specific heat has several peaks, which correspond to ordering processes in different energy scales. In particular, magnetic order appears at very low temperature. Depending on the chemical potential of the particle bath and the Coulomb interaction, the system exhibits an itinerant ferromagnetic state or an antiferromagnetic state of the Mott insulator. Microscopically the competition between these two types of orderings causes a peculiar ordering process of local spin correlations. Some local ferromagnetic correlations are found to be robust, which indicates that the ferromagnetic correlation originates from the motion of itinerant electrons in a short-range cluster.