arXiv:cond-mat/0403364 · Physical Review Letters
Excitation Hierarchy of the Quantum Sine-Gordon Spin Chain in a Strong Magnetic Field
Sergei A. Zvyagin, Alexei K. Kolezhuk, J. Krzystek, R. Feyerherm
Abstract
The magnetic excitation spectrum of copper pyrimidine dinitrate, a material containing S = 1 / 2 antiferromagnetic chains with alternating g tensor and the Dzyaloshinskii-Moriya interaction and exhibiting a field-induced spin gap, is probed using submillimeter wave electron spin resonance spectroscopy. Ten excitation modes are resolved in the low-temperature spectrum, and their frequency-field diagram is systematically studied in magnetic fields up to 25 T. The experimental data are sufficiently detailed to make a very accurate comparison with predictions based on the quantum sine-Gordon field theory. Signatures of three breather branches and a soliton, as well as those of several multiparticle excitation modes, are identified.