Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We present results of high-frequency/field Electron Spin Resonance (ESR) studies of the highly frustrated spin system SrCu₂(BO₃)₂,which can be regarded as to the best known realization of the Shastry-Sutherland model for two-dimensional Heisenberg antiferromagnets. The frequency-field diagram of magnetic excitations has been studied in a frequency range of 150-700 GHz, employing unable-frequency ESR technique. Two gapped odes were observed in the excitation spectrum. The size of the quantum spin gaps determined directly is: 708 GHz and 764 GHz (34 K and 36.7 K). The observation of excitations from the ground state (which are normally forbidden) and a double-gap structure of the ESR excitation spectrum in SrCu₂(BO₃)₂ suggest and essential role of the Dzyaloshinski-Moriya interaction. The results are compared with those obtained by Nojiri et al. [J. Phys. Soc. Jpn. 68, 2906 (1999); J.Phys. Soc. Jpn. 72, 3243 (2003)]. The temperature behavior of excited-state transitions in SrCu₂(BO₃)₂ (ESR linewidth and intensity) is presented and discussed.