Anisotropic exchange within decoupled tetrahedra in the quantum breathing pyrochlore Ba3Yb2Zn5O11

TL;DR

This study investigates the low-energy spin excitations in the breathing pyrochlore Ba3Yb2Zn5O11 using neutron scattering and a theoretical model of isolated Yb3+ tetrahedra, revealing complex anisotropic exchanges and predicting an octupolar paramagnet.

Contribution

The paper introduces a detailed anisotropic exchange model for Yb3+ tetrahedra in Ba3Yb2Zn5O11 that accurately reproduces experimental data and predicts novel magnetic behavior.

Findings

Observation of nearly resolution limited modes at 250 mK

Model reproduces neutron scattering, heat capacity, and susceptibility data

Prediction of an octupolar paramagnet at low temperatures

Abstract

The low energy spin excitation spectrum of the breathing pyrochlore Ba3Yb2Zn5O11 has been investigated with inelastic neutron scattering. Several nearly resolution limited modes with no observable dispersion are observed at 250 mK while, at elevated temperatures, transitions between excited levels become visible. To gain deeper insight, a theoretical model of isolated Yb3+ tetrahedra parametrized by four anisotropic exchange constants is constructed. The model reproduces the inelastic neutron scattering data, specific heat, and magnetic susceptibility with high fidelity. The fitted exchange parameters reveal a Heisenberg antiferromagnet with a very large Dzyaloshinskii-Moriya interaction. Using this model, we predict the appearance of an unusual octupolar paramagnet at low temperatures and speculate on the development of inter-tetrahedron correlations.