Low-Energy Excitations and Ground State Selection in Quantum Breathing Pyrochlore Antiferromagnet Ba$_3$Yb$_2$Zn$_5$O$_{11}$

TL;DR

This study investigates low-energy excitations in the quantum breathing pyrochlore antiferromagnet Ba$_3$Yb$_2$Zn$_5$O$_{11}$ using neutron scattering and thermodynamic measurements, revealing ground state selection mechanisms at ultra-low temperatures.

Contribution

The paper combines experimental neutron scattering and thermodynamic data with a spin-1/2 tetrahedron model to explain excitations and ground state selection in Ba$_3$Yb$_2$Zn$_5$O$_{11}$.

Findings

INS spectra explained by a spin-1/2 tetrahedron model with anisotropy and Dzyaloshinskii-Moriya interaction

Magnetization and heat capacity well reproduced at higher temperatures

Observation of a broad heat capacity maximum at 63 mK indicating ground state selection

Abstract

We study low energy excitations in the quantum breathing pyrochlore antiferromagnet Ba$_3$Yb$_2$Zn$_5$O$_{11}$ by combination of inelastic neutron scattering (INS) and thermodynamical properties measurements. The INS spectra are quantitatively explained by spin-1/2 single-tetrahedron model having $XXZ$ anisotropy and Dzyaloshinskii-Moriya interaction. This model has a two-fold degeneracy of the lowest-energy state per tetrahedron and well reproduces the magnetization curve at 0.5 K and heat capacity above 1.5 K. At lower temperatures, however, we observe a broad maximum in the heat capacity around 63 mK, demonstrating that a unique quantum ground state is selected due to extra perturbations with energy scale smaller than the instrumental resolution of INS.