title: Direct determination of exchange parameters in Cs2CuBr4 and Cs2CuCl4: high-field electron-spin-resonance studies.
abstract: Spin-1/2 Heisenberg antiferromagnets Cs2CuCl4 and Cs2CuBr4 with distorted triangular-lattice structures are studied by means of electron spin resonance spectroscopy in magnetic fields up to the saturation field and above. In the magnetically saturated phase, quantum fluctuations are fully suppressed, and the spin dynamics is defined by ordinary magnons. This allows us to accurately describe the magnetic excitation spectra in both materials and, using the harmonic spin-wave theory, to determine their exchange parameters. The viability of the proposed method was proven by applying it to Cs2CuCl4, yielding J/kB=4.7(2)  K, J'/kB=1.42(7)  K, [J'/J≃0.30] and revealing good agreement with inelastic neutron-scattering results. For the isostructural Cs2CuBr4, we obtain J/kB=14.9(7)  K, J'/kB=6.1(3)  K, [J'/J≃0.41], providing exact and conclusive information on the exchange couplings in this frustrated spin system.
authors.affiliation: Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany.
authors.forename: S A
authors.initials: SA
authors.lastname: Zvyagin
authors.affiliation: Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Kamenskyi
authors.affiliation: Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Ozerov
authors.affiliation: Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany and Institüt fur Festkörperphysik, TU Dresden, 01068 Dresden, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Wosnitza
authors.affiliation: KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Ikeda
authors.affiliation: KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Fujita
authors.affiliation: KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Hagiwara
authors.affiliation: P.L. Kapitza Institute for Physical Problems, RAS, 119334 Moscow, Russia.
authors.forename: A I
authors.initials: AI
authors.lastname: Smirnov
authors.affiliation: Moscow Institute for Physics and Technology, 141700 Dolgoprudnyi, Russia.
authors.forename: T A
authors.initials: TA
authors.lastname: Soldatov
authors.affiliation: A.V. Shubnikov Institute of Crystallography, RAS, 119333, Moscow, Russia.
authors.forename: A Ya
authors.initials: AY
authors.lastname: Shapiro
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA.
authors.forename: J
authors.initials: J
authors.lastname: Krzystek
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: R
authors.initials: R
authors.lastname: Hu
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA and Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA.
authors.forename: H
authors.initials: H
authors.lastname: Ryu
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA and Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA.
authors.forename: C
authors.initials: C
authors.lastname: Petrovic
authors.affiliation: Service de Physique Statistique, Magnétisme et Supraconductivité, UMR-E9001 CEA-INAC/UJF, 38054 Grenoble Cedex 9, France.
authors.forename: M E
authors.initials: ME
authors.lastname: Zhitomirsky