Non Fermi Liquid behavior in the under-screened Kondo model

TL;DR

This paper reveals that the under-screened Kondo model exhibits non-Fermi liquid behavior due to residual ferromagnetic interactions, leading to a singular Fermi liquid state with distinctive thermodynamic properties.

Contribution

It introduces a novel perspective on the physics of partially screened magnetic moments using Schwinger bosons, showing the destabilization of Fermi liquid behavior and its tunability with magnetic field.

Findings

Residual ferromagnetic interaction causes non-Fermi liquid behavior.

Magnetic field restores Fermi liquid properties with a field-dependent Fermi temperature.

Specific heat coefficient diverges as 1/(T ln^4(T_K/T)) at low temperatures.

Abstract

Using the Schwinger boson spin representation, we reveal a new aspect to the physics of a partially screened magnetic moment in a metal, as described by the spin $S$ Kondo model. We show that the residual ferromagnetic interaction between a partially screened spin and the electron sea destabilizes the Landau Fermi liquid, forming a singular Fermi liquid with a $1/ (T \ln ^{4} (T_{K}/T))$ divergence in the low temperature specific heat coefficient $C_{V}/T$. A magnetic field $B$ tunes this system back into Landau Fermi liquid with a Fermi temperature proportional to $B \ln^2 (T_K/B)$. We discuss a possible link with field-tuned quantum criticality in heavy electron materials.