Ground-state degeneracy and low-temperature thermodynamics of correlated electrons on highly frustrated lattices

TL;DR

This paper explores the ground-state degeneracy and low-temperature thermodynamics of correlated electrons on highly frustrated lattices, revealing macroscopic degeneracy and characteristic thermodynamic signatures through analytical and numerical methods.

Contribution

It introduces a method to compute ground-state degeneracies in models with flat bands and discusses their thermodynamic implications, supported by numerical exact diagonalization results.

Findings

Macroscopic ground-state degeneracy in frustrated lattice models

Presence of a low-temperature peak in specific heat

Validation of analytical results with numerical exact diagonalization

Abstract

Highly frustrated lattices yield a completely flat lowest single-electron band. Remarkably, exact many-body ground states can be constructed for the repulsive Hubbard model and the t-J model by filling this flat band with localized electron states. This construction leads to a macroscopic ground-state degeneracy. We discuss how to compute these ground-state degeneracies for a certain class of models, including in particular the sawtooth chain. Furthermore, we discuss generic consequences for low-temperature thermodynamic properties, like the appearance of a low-temperature peak in the specific heat. Finally, we present complementary numerical results obtained by exact diagonalization.