Probing Flat Band Physics in Spin Ice Systems via Polarized Neutron Scattering

TL;DR

This paper demonstrates how polarized neutron scattering can effectively probe flat band spin correlations in frustrated magnetic systems like spin ice, revealing subtle effects of perturbations on flat band degeneracy.

Contribution

It introduces a method to isolate flat band spin correlations using polarized neutron scattering and explains its application to real spin ice materials.

Findings

NSF scattering is sensitive to weak perturbations lifting flat band degeneracy.

Flat bands produce dispersionless responses in NSF neutron scattering.

Experimental data on Ho2Ti2O7 shows dispersive NSF scattering, explained by the model.

Abstract

In this paper, we illustrate how polarized neutron scattering can be used to isolate the spin-spin correlations of modes forming flat bands in a frustrated magnetic system hosting a classical spin liquid phase. In particular, we explain why the nearest-neighbor spin ice model, whose interaction matrix has two flat bands, produces a dispersionless (i.e. "flat") response in the non-spin-flip (NSF) polarized neutron scattering channel, and demonstrate that NSF scattering is a highly sensitive probe of correlations induced by weak perturbations which lift the flat band degeneracy. We use this to explain the experimentally measured dispersive (i.e. non-flat) NSF channel of the dipolar spin ice compound $\mathrm{Ho}_2 \mathrm{Ti}_2 \mathrm{O}_7$.