Metallic Ferromagnetism in the Kondo Lattice

TL;DR

This paper provides a rigorous analysis of metallic ferromagnetism in the Kondo lattice, revealing a strongly coupled ferromagnetic phase with a small Fermi surface and non-Fermi liquid behavior, addressing longstanding theoretical gaps.

Contribution

It offers an asymptotically exact theoretical framework for understanding ferromagnetism in the Kondo lattice, a problem previously lacking rigorous solutions.

Findings

Ferromagnetic order is strongly coupled with a small Fermi surface.

Non-Fermi liquid behavior appears over a range of frequencies and temperatures.

Provides insights into long-standing puzzles in heavy fermion ferromagnetic metals.

Abstract

Metallic magnetism is both ancient and modern, occurring in such familiar settings as the lodestone in compass needles and the hard drive in computers. Surprisingly, a rigorous theoretical basis for metallic ferromagnetism is still largely missing. The Stoner approach perturbatively treates Coulomb interactions when the latter need to be large, while the Nagaoka approach incorporates thermodynamically negligible electrons into a half-filled band. Here, we show that the ferromagnetic order of the Kondo lattice is amenable to an asymptotically exact analysis over a range of interaction parameters. In this ferromagnetic phase, the conduction electrons and local moments are strongly coupled but the Fermi surface does not enclose the latter (i.e. it is small). Moreover, non-Fermi liquid behavior appears over a range of frequencies and temperatures. Our results provide the basis to understand some long-standing puzzles in the ferromagnetic heavy fermion metals, and raises the prospect for a new class of ferromagnetic quantum phase transitions.