Magnetic Order with Fractionalized Excitations in Pyrochlore Magnets with Strong Spin-Orbit Coupling

Li Ern Chern,Yong Baek Kim

doi:10.1038/s41598-019-47517-6

Abstract

A recent inelastic neutron scattering experiment on the pyrochlore magnet Yb2Ti2O7 uncovers an unusual scattering continuum in the spin excitation spectrum despite the splayed ferromagnetic order in the ground state. While there exist well defined spin wave excitations at high magnetic fields, the one magnon modes and the two magnon continuum start to strongly overlap upon decreasing the field, and eventually they become the scattering continuum at zero field. Motivated by these observations, we investigate the possible emergence of a magnetically ordered ground state with fractionalized excitations in the spin model with the exchange parameters determined from two previous experiments. Using the fermionic parton mean field theory, we show that the magnetically ordered state with fractionalized excitations can arise as a stable mean field ground state in the presence of sufficiently strong quantum fluctuations. The spin excitation spectrum in such a ground state is computed and shown to have the scattering continuum. Upon increasing the field, the fractionalized magnetically ordered state is suppressed, and is eventually replaced by the conventional magnetically ordered phase at high fields, which is consistent with the experimental data. We discuss further implications of these results to the experiments and possible improvements on the theoretical analysis.

Highlights

The family of rare earth pyrochlore compounds is the exemplar of three dimensional frustrated magnets that offer tremendous opportunities for the discovery of exotic phases of matter
With this picture in mind, we investigate in this work the possibility of a quantum spin liquid coexisting with a magnetic order, where the ground state is magnetically ordered, but the deconfined spinons exist as elementary excitations
Our results demonstrate that the low lying excitation continuum observed in the recent inelastic neutron scattering experiment[20] on Yb2Ti2O7 at weak magnetic fields may be attributed to deconfined spinons in the fractionalized magnetically ordered phase

Summary

Introduction

The family of rare earth pyrochlore compounds is the exemplar of three dimensional frustrated magnets that offer tremendous opportunities for the discovery of exotic phases of matter. Many other pyrochlore compounds, such as Yb2Ti2O7, Yb2Sn2O7, Tb2Ti2O7, and Pr2Zr2O7 5, to name a few, are characterized by strong quantum fluctuations and complex exchange interactions. They are less understood and currently still under intense experimental and theoretical investigations. It is conceivable that the two spinon continuum could be seen above the small confinement energy scale, providing an alternative description of the scattering continuum seen in the experiment With this picture in mind, we investigate in this work the possibility of a quantum spin liquid coexisting with a magnetic order, where the ground state is magnetically ordered, but the deconfined spinons exist as elementary excitations.

Methods

Results

Conclusion