Direct measurement of the Bose-Einstein condensation universality class in NiCl2-4SC(NH2)2 at ultralow temperatures |
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Authors: | Yin L Xia J S Zapf V S Sullivan N S Paduan-Filho A |
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Institution: | Department of Physics, University of Florida, and National High Magnetic Field Laboratory, Gainesville, Florida 32611-8440, USA. |
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Abstract: | In this work, we demonstrate field-induced Bose-Einstein condensation (BEC) in the organic compound NiCl2-4SC(NH2)_{2} using ac susceptibility measurements down to 1 mK. The Ni S=1 spins exhibit 3D XY antiferromagnetism between a lower critical field H_{c1} approximately 2 T and a upper critical field H_{c2} approximately 12 T. The results show a power-law temperature dependence of the phase transition line H_{c1}(T)-H_{c1}(0)=aT;{alpha} with alpha=1.47+/-0.10 and H_{c1}(0)=2.053 T, consistent with the 3D BEC universality class. Near H_{c2}, a kink was found in the phase boundary at approximately 150 mK. |
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