Disorder-enhanced delocalization and local-moment quenching in a disordered antiferromagnet

TL;DR

This paper investigates how disorder influences magnetic properties in a disordered antiferromagnet, revealing disorder can enhance delocalization and suppress local moments, with a crossover at a critical disorder strength.

Contribution

It introduces a unified paradigm explaining disorder-enhanced delocalization and local-moment quenching in disordered antiferromagnets, including quantum corrections and damping effects.

Findings

Disorder decreases the energy gap but leaves sublattice magnetization unchanged in weak disorder.

Magnon energies and Neel temperature increase with disorder in the strong correlation limit.

A crossover at W ~ U leads to local moment quenching and spin vacancy formation.

Abstract

The interplay of disorder and spin-fluctuation effects in a disordered antiferromagnet is studied. In the weak-disorder regime (W \le U), while the energy gap decreases rapidly with disorder, the sublattice magnetization, including quantum corrections, is found to remain essentially unchanged in the strong correlation limit. Magnon energies and Neel temperature are enhanced by disorder in this limit. A single paradigm of disorder-enhanced delocalization qualitatively accounts for all these weak disorder effects. Vertex corrections and magnon damping, which appear only at order (W/U)^4, are also studied. With increasing disorder a crossover is found at W \sim U, characterized by a rapid decrease in sublattice magnetization due to quenching of local moments, and formation of spin vacancies. The latter suggests a spin-dilution behavior, which is indeed observed in softened magnon modes, lowering of Neel temperature, and enhanced transverse spin fluctuations.