Magnetotransport in the Kondo model with ferromagnetic exchange interaction

TL;DR

This paper investigates the transport properties of a ferromagnetic Kondo model with spin-1/2 impurities under magnetic fields, revealing low-energy anomaly splitting consistent with recent experiments on quantum dots.

Contribution

It combines Majorana diagrammatic theory with NRG simulations to analyze ferromagnetic Kondo effects, extending understanding beyond antiferromagnetic cases.

Findings

Ferromagnetic Kondo interaction is marginally irrelevant, allowing perturbative analysis.

The low-energy Kondo anomaly splits at small Zeeman energies.

Results align with experimental observations in spin-1 quantum dots.

Abstract

We consider the transport properties in an applied magnetic field of the spin S=1/2 Kondo model with ferromagnetic exchange coupling to electronic reservoirs, a description relevant for the strong coupling limit of underscreened spin S=1 Kondo impurities. Because the ferromagnetic Kondo interaction is marginally irrelevant, perturbative methods should prove accurate down to low energies. For the purpose of this study, we use a combination of Majorana diagrammatic theory with Density Matrix Numerical Renormalization Group simulations. In the standard case of antiferromagnetic Kondo exchange, we first show that our technique recovers previously obtained results for the T-matrix and spin relaxation at weak coupling (above the Kondo temperature). Considering then the ferromagnetic case, we demonstrate how the low-energy Kondo anomaly splits for arbitrary small values of the Zeeman energy, in contrast to fully screened Kondo impurities near the strong coupling Fermi liquid fixed point, and in agreement with recent experimental findings for spin S=1 molecular quantum dots.