Critical behavior and spin dynamics of Heisenberg antiferromagnetic spin chains in high magnetic fields

• Applicant: Dr. Sergei Zvyagin
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2007 to 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 47714691

The research program aims to test recent theoretical predictions focused on understanding magnetic properties of low-dimensional magnets, with the main emphasis placed on investigations of the spin dynamics and the magnetic excitation spectrum in novel S = 1/2 and S = 1 Heisenberg antiferromagnets in high magnetic fields. Specifically, the fundamental questions and issues to be addressed include the study of magnon excitations in the field-induced Bose-Einstein-condensation phase in NiCl2-4SC(NH2)2, magnetic properties and the elementary excitation spectrum in novel Haldane chains, antiferromagnetic spin-1 chains with strong anisotropy (large-D chains), and spin-1/2 Heisenberg chains. The role of a field-induced staggered magnetization (caused by the Dzyaloshinskii-Moriya interactions and/or alternating g-tensor) in antiferromagnetic S = 1/2 and S = 1 chains will be explored in connection to a number of recently discovered unusual phenomena, including changes in selection rules for nominally forbidden transitions, creation of fieldinduced incommensurate states, opening of gaps in the excitation spectrum, and the formation of solitons and their bound states, breathers. Our emphasis will be placed on a detailed comparison of experimental data and theory (including the generalized spin-wave theory, the Lieb-Mattis model, and the sine-Gordon quantum-field-theoretical approach by Oshikawa and Affleck, etc.), currently available for quantum magnets in high magnetic fields.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Joachim Wosnitza