title: Static and Dynamical Properties of the Spin-1/2 Equilateral Triangular-Lattice Antiferromagnet Ba_{3}CoSb_{2}O_{9}.
abstract: We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba_{3}CoSb_{2}O_{9}. Besides confirming that the Co^{2+} magnetic moments lie in the ab plane for zero magnetic field and then determining all the exchange parameters of the minimal quasi-2D spin Hamiltonian, we provide conclusive experimental evidence of magnon decay through observation of intrinsic line broadening. Through detailed comparisons with the linear and nonlinear spin-wave theories, we also point out that the large-S approximation, which is conventionally employed to predict magnon decay in noncollinear magnets, is inadequate to explain our experimental observation. Thus, our results call for a new theoretical framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects.
authors.affiliation: Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.|Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: J
authors.initials: J
authors.lastname: Ma
authors.affiliation: iTHES Research Group and Condensed Matter Theory Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kamiya
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Tao
authors.initials: T
authors.lastname: Hong
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: H B
authors.initials: HB
authors.lastname: Cao
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: G
authors.initials: G
authors.lastname: Ehlers
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: W
authors.initials: W
authors.lastname: Tian
authors.affiliation: Theoretical Division, T-4 and CNLS, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: Batista
authors.affiliation: Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Z L
authors.initials: ZL
authors.lastname: Dun
authors.affiliation: Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.|National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310-3706, USA.
authors.forename: H D
authors.initials: HD
authors.lastname: Zhou
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: M
authors.initials: M
authors.lastname: Matsuda