Magnetic properties of strongly disordered electronic systems

TL;DR

This paper reviews the magnetic properties of strongly disordered electronic systems, focusing on local magnetic moments, quantum Griffiths phenomena, and the transition to metallic spin glass states, with implications for doped semiconductors and heavy-fermion materials.

Contribution

It provides a unified perspective on magnetic behavior in disordered metals, emphasizing the role of quantum Griffiths effects and mean-field theory of spin glass transitions.

Findings

Disordered Fermi liquids are unstable towards local magnetic moment formation.

Quantum Griffiths phenomena are key precursors to quantum phase transitions.

Mean-field theory describes the transition to metallic spin glass states.

Abstract

We present a unified, global perspective on the magnetic properties of strongly disordered electronic systems, with special emphasis on the case where the ground state is metallic. We review the arguments for the instability of the disordered Fermi liquid state towards the formation of local magnetic moments, and argue that their singular low temperature thermodynamics are the ``quantum Griffiths'' precursors of the quantum phase transition to a metallic spin glass; the local moment formation is therefore not directly related to the metal-insulator transition. We also review the the mean-field theory of the disordered Fermi liquid to metallic spin glass transition and describe the separate regime of ``non-Fermi liquid'' behavior at higher temperatures near the quantum critical point. The relationship to experimental results on doped semiconductors and heavy-fermion compounds is noted.