Magnetic excitations and the field-induced condensation of magnons in the large-D spin-1 chain system DTN

NiCl2-4SC(NH2)2 (DTN) is a quantum spin-1 chain system with strong easy-pane anisotropy and a new material for studying the magnon condensation in magnetic fields. In this talk, I will present tunablefrequency electron spin resonance (ESR) studies of magnetic excitations in DTN in fields up to 25 T. First, I am going to show how the high-field ESR can be used for describing the temperature-field phase diagram and the low-temperature magnetization data in the field-induced ordered phase of DTN. Second, I will report on the first conclusive observation of the two-magnon bound states, which is a unique feature of the high-field spin-polarized phase of spin-1 large-D Heisenberg chains. Third, based on the analysis of the ESR data, I am going to discuss the relevance of the underlying physics in DTN to the field-induced Bose-Einstein Condensation phenomenon in quantum antiferromagnets. Finally, I will briefly talk about recent developments of the high-field ESR Program at the Dresden High Magnetic Field Laboratory.