Condensed-Matter Physics & Materials Science Seminar

Spin dynamics in triangular-lattice antiferromagnets Cs2CuBr4 and Cs2CuCl4: high-field ESR studies Sergei Zvyagin Dresden High Magnetic Field Laboratory (HLD) Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany A spin-1/2 Heisenberg antiferromagnet (AF) on a triangular lattice is the paradigmatic model in quantum magnetism and in the focus of recent experimental and theoretical studies. Here, we present results of high-field electron spin resonance (ESR) studies of spin-1/2 Heisenberg AFs Cs2CuCl4 and Cs2CuBr4 with distorted triangular-lattice structures in magnetic fields up to 50 T [1]. 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 approach has a broader impact and can be potentially used for any quantum magnet with reduced (e.g., by the staggered Dzyaloshinskii-Moriya interaction) translational symmetry, resulting, as predicted, in emergence of a new exchange mode above Hsat. We found that a substantial zero-field energy gap, Î"~9.5 K, observed in the low-temperature excitation spectrum of Cs2CuBr4, is present below and well above TN, being a characteristics of low-dimensional spin-correlated state. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangular lattice AF. This work was supported by the DFG. [1] S. A. Zvyagin, D. Kamenskyi, M. Ozerov, J. Wosnitza, M. Ikeda, T. Fujita, M. Hagiwara, A. I. Smirnov, T. A. Soldatov, A. Ya. Shapiro, J. Krzystek, R. Hu, H. Ryu, C. Petrovic, and M. E. Zhitomirsky, Phys. Rev. Lett. 112, 077206, 2014