Partial localization of correlated electrons: spin dependent masses, saturated ferromagnetism, and effective s-d model

TL;DR

This paper investigates how correlated electrons partially localize in a model with orbitally degenerate bands, leading to spin-dependent masses, ferromagnetism, and an effective s-d model, highlighting the role of Hund's coupling and electron correlations.

Contribution

It introduces a detailed analysis of the localization transition in orbitally degenerate systems and derives an effective s-d model describing the coexistence of localized and itinerant electrons.

Findings

Spin-dependent quasiparticle masses in ferromagnetic phase

Saturation of ferromagnetism driven by Hund's rule coupling

Metamagnetic transition induced by electron correlations

Abstract

We determine the localization threshold in a partially filled and orbitally degenerate model of correlated electrons. Particular emphasis is put on a non-integer band filling, when the system decomposes into the localized and the itinerant subsystems; this situation is described by an effective s-d model. A simultaneous transition to the ferromagnetic state is discussed as driven by the Hund's rule coupling. Dependence of the quasiparticle mass on the spin direction appears naturally in the ferromagnetic phase and is attributed to the electron correlation effects, as is also a metamagnetic transition in an applied field. Although the main results have been obtained within the saddle point slave-boson approach, their qualitative features are discussed in general terms, i.e. as a transition from quantum-mechanical indistinguishability of particles to the two-component situation. A comparison with the situation for the orbitally nondegenerate band is also briefly mentioned.