Interacting Fermions, Boundaries, and Finite Size Effects

TL;DR

This paper investigates how finite size effects influence the thermodynamics of strongly interacting fermions, using an effective field theory, and explores implications for the Casimir effect in layered fermionic materials.

Contribution

It provides a detailed analytical and numerical analysis of finite size effects on fermionic thermodynamics within an effective field theory framework, including new regularization and expansion techniques.

Findings

Finite size shifts critical temperatures and transition orders.

Analytic expressions for thermodynamic potential in various regimes.

Numerical results confirm finite size effects are significant.

Abstract

In this work we analyze how effects of finite size may modify the thermodynamics of a system of strongly interacting fermions that we model using an effective field theory with four-point interactions at finite temperature and density and look in detail at the case of a confining two-layer system. We compute the thermodynamic potential in the large-$N$ and mean-field approximations and adopt a zeta-function regularization scheme to regulate the divergences. Explicit expansions are obtained in different regimes of temperature and separation. The analytic structure of the potential is carefully analyzed and relevant integral and series representations for the various expressions involved are obtained. Several known results are obtained as limiting case of general results. We numerically implement the formalism and compute the thermodynamic potential, the critical temperature and the fermion condensate showing that effects of finite size tend to shift the critical points and the order of the transitions. The present discussion may be of some relevance for the study of the Casimir effect between strongly coupled fermionic materials with inter-layer interactions.