Magnetic solitons in quantum spin chains

The first documentary observation of solitons was done in 1834 by John Scott Russell on Union Canal in Scot-land, UK, who found that a heap of water in a canal propagates undistorted over several kilometers. Nowadays, a large number of soliton manifestations is known, including for instance solitons in fiber-optics communication systems, solitons in conducting polymers, low-frequency collective motion in proteins and DNA, etc. Many types of solitons can be described using the famous sine-Gordon equation... The sine-Gordon equation can be solved exactly, with solitons and their bound states, breathers, as solution. In this presentation I will talk about magnetic solitary waves in quantum spin chains, probed in copper pyrimidine dinitrate (Cu-PM, which is a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions) by means of high-frequency and high-field Electron Spin Resonance (ESR) spectroscopy. Signa-tures of three breather branches and a soliton were identified, as predicted by the sine-Gordon quantum-field theory. Having a fully quantum-mechanical nature, the solitary waves in quantum spin chains can be destroyed by thermal fluctuations. This can be nicely illustrated by analyzing the parameters of ESR spectra using a new theoretical concept by Oshikawa and Affleck. Finally, I will show the crucial effect of high magnetic fields sup-pressing the solitary-wave behavior and transforming the soliton-breather excitation spectrum into magnons. These studies were done employing ESR technique in pulsed magnetic fields up to 64 T. Excellent agreement between the theory and experiment in all cases was obtained. In addition, the development of the high-field Elec-tron Spin Resonance facilities at the Dresden High Magnetic Field Laboratory will be presented.