Magnetic field induced mixed-level Kondo effect in two-level systems

TL;DR

This paper investigates how an in-plane magnetic field induces a mixed-level Kondo effect in a two-orbital impurity system, revealing a finite-field conductance peak and detailed properties via numerical renormalization group analysis.

Contribution

It provides a comprehensive characterization of the mixed-level Kondo state in two-orbital systems under magnetic fields using numerical renormalization group methods.

Findings

Spectral function develops a Fermi level resonance at finite Zeeman field

Linear conductance peaks at a specific Zeeman field and decreases with temperature

Impurity system exhibits Kondo-like local moment and entropy behavior

Abstract

We consider a two-orbital impurity system with intra and inter-level Coulomb repulsion that is coupled to a single conduction channel. This situation can generically occur in multilevel quantum dots or in systems of coupled quantum dots. For finite energy-spacing between spin-degenerate orbitals, an in-plane magnetic field drives the system from a local singlet ground state to a "mixed-level" Kondo regime, where the Zeeman-split levels are degenerate for opposite spin states. We use the numerical renormalization group approach to fully characterize this mixed level Kondo state and discuss its properties in terms of the applied Zeeman field, temperature and system parameters. Under suitable conditions, the total spectral function is shown to develop a Fermi level resonance, so that the linear conductance of the system peaks at a finite Zeeman field while it decreases as function of temperature. These features, as well as the local moment and entropy contribution of the impurity system are commensurate with Kondo physics, which can be studied in suitably tuned quantum dot systems.