Structure of the magnetic excitations in the spin-1/2 triangular-lattice Heisenberg antiferromagnet Ba3CoSb2O9

Saya Ito,Nobuyuki Kurita,Kazuhisa Kakurai,Shinichi Itoh,Kenji Nakajima,Keitaro Kuwahara,Hidekazu Tanaka,Seiko Ohira-Kawamura

doi:10.1038/s41467-017-00316-x

Abstract

A spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) is a prototypical frustrated quantum magnet, which exhibits remarkable quantum many-body effects that arise from the synergy between spin frustration and quantum fluctuation. The ground-state properties of a spin-1/2 TLHAF are theoretically well understood. However, the theoretical consensus regarding the magnetic excitations is limited. The experimental study of the magnetic excitations in spin-1/2 TLHAFs has also been limited. Here we show the structure of magnetic excitations in the spin-1/2 TLHAF Ba3CoSb2O9 investigated by inelastic neutron scattering. Significantly different from theoretical expectations, the excitation spectrum has a three-stage energy structure. The lowest-energy first stage is composed of dispersion branches of single-magnon excitations. The second and third stages are dispersive continua accompanied by a columnar continuum extending above 10 meV, which is six times larger than the exchange interaction J = 1.67 meV. Our results indicate the shortcomings of the current theoretical framework.

Highlights

Remarkable features of magnetic excitations in Ba3CoSb2O9 are the two strong dispersive excitation continua, in which the higher energy excitation continuum extends to over the energy of 6 J
The scattering data were collected at 1.0 K, well below TN = 3.8 K, with incident neutron energies of Ei = 3.14 and 7.74 meV. These two a 3 (meV)
Two weak Q-independent spectra between 5 and 6 meV in Fig. 1b, d are extrinsic spectra, which stem from γ-rays emitted by the collision of neutrons with Ei = 4.68 meV to objects made of cadmium or boron in the beam line

Summary

Introduction

Remarkable features of magnetic excitations in Ba3CoSb2O9 are the two strong dispersive excitation continua, in which the higher energy excitation continuum extends to over the energy of 6 J. The entire magnetization curve, including a high-field quantum phase transition above the 1/3-plateau[18], has been explained quantitatively by taking the weak easy-plane anisotropy and interlayer exchange interaction into account[19, 20].

Results

Conclusion