Magnetic excitations in the BEC candidate DTN: high-field ESR studies


Magnetic excitations in the BEC candidate DTN: high-field ESR studies

Zvyagin, S.

NiCl2-4SC(NH2)2 (known as DTN) is a quantum S = 1 chain system with strong easy-plane anisotropy that is regarded as a new candidate for the Bose-Einstein condensation (BEC) of magnons, with critical fields Bc1 = 2.1 T, Bc2 = 12.6 T (defined at T = 0). Electron Spin Resonance (ESR) studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode observed in the high-field spin-polarized phase at temperatures above Tc (Tc ≤ 1.2 K), a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8.9 K, Jc = 2.2 K, and Ja,b = 0.18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Furthermore, we present a systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase at temperatures down to 0.45 K. We argue that two gapped modes observed in the experiment can be consistently interpreted within a four-sublattice antiferromagnet model with a finite interaction between two tetragonal subsystems and unbroken axial symmetry. The latter is of crucial importance for the interpretation of the field-induced ordering in DTN in terms of the BEC of magnons.

  • Invited lecture (Conferences)
    Correlated Electron Systems in High Magnetic Fields, 13.-17.10.2008, Dresden, Deutschland

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Publ.-Id: 11845