Schwinger boson mean field perspective on emergent spins in diluted Heisenberg antiferromagnets

TL;DR

This paper applies Schwinger boson mean field theory to study low-energy spin excitations and emergent local moments in diluted antiferromagnets on square and Bethe lattices, revealing insights into magnetic order and interactions.

Contribution

It introduces an adapted SBMFT approach for nonuniform systems to explain emergent local moments and their interactions in diluted antiferromagnets.

Findings

Emergent local moments develop on dilution due to sublattice imbalance.

Low-frequency single particle excitations are linked to local moment formation.

The energy scale of interactions between emergent moments aligns with many-body calculations.

Abstract

Using an adaptation of Schwinger boson mean field theory (SBMFT) for nonuniform systems, we study the nature of low-energy spin excitations on the square and Bethe lattice at their percolation threshold. The optimal SBMFT parameters are interpreted as on-site potentials and pairing amplitudes, which enables an explanation of why emergent local moments develop in this system on dilution [L. Wang and A. W. Sandvik, Phys. Rev. Lett. 97, 117204 (2006); H.J. Changlani et al., ibid 111, 157201 (2013)] and why the corresponding single particle frequencies are driven to anomalously low values. We discuss how our mean field calculations suggest the strong link between the presence of sublattice imbalance and long range antiferromagnetic order, and why linear spin wave theory is inadequate for capturing this relation. Within the SBMFT framework, we also extract an energy scale for the interaction between emergent moments, which show qualitative agreement with many-body calculations.