Interacting Quantum Dot Coupled to a Kondo Spin: A Universal Hamiltonian Study

TL;DR

This paper investigates how a Kondo spin influences the ferromagnetic exchange-driven spin transitions in a mesoscopic quantum dot, revealing complex shifts in the Stoner staircase through numerical and analytical methods.

Contribution

It provides a detailed analysis of the interplay between Kondo coupling and ferromagnetic exchange in quantum dots using a universal Hamiltonian framework, including numerical and analytical solutions.

Findings

Kondo interaction modifies the Stoner staircase in quantum dots.

Weak Kondo coupling shifts spin-transition steps to lower exchange values.

Strong Kondo coupling reverses the shift, moving steps to higher exchange values.

Abstract

We study a mesoscopic interacting quantum dot described by the "universal Hamiltonian" that is coupled to a Kondo spin. The ferromagnetic exchange interaction within the dot leads to a stepwise increase of the ground state spin; this Stoner staircase is modified non-trivially by the Kondo interaction. We find that the spin-transition steps move to lower values of the exchange coupling for weak Kondo interaction, but shift back up for sufficiently strong Kondo coupling. The problem is solved numerically by diagonalizing the system Hamiltonian in a customized good-spin basis and analytically in the weak and strong Kondo coupling limits. The interplay of Kondo and ferromagnetic exchange can be probed with experimentally tunable parameters.