Spin excitations in S = 1/2 antiferromagnetic chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction

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 multi-frequency electron spin resonance spectroscopy in magnetic fields up to 25 T. Signatures of three breather branches an a soliton, as well as those of several multi-particle excitation modes are identified, and their frequency-field dependences are described in frame of the quantum sine-Gordon field theory. In addition, a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)] ist tested. Their theory, based on bosonization and the self-energy formalism, can be applied for precise calculation of ESR parameters of s = 1/2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained. Results are published in S.A. Zvyagin et al., Phys. Rev. Lett. 93, 027201 (2004);ibid. Phys. Rev. Lett. 95, 012707 (2005).