Electron Spin Resonance in sine-Gordon Spin Chains in the Perturbative Spinon Regime

We report on low-temperature multi-frequency ESR studies of coopper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, allowing us to test a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)]. 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 of the presentation are published in: S.A. Zvyagin et al., Phys. Rev. Lett. 95, 017207, 2005.