Dresden 2011 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 35: CE: Low-dimensional Systems - Materials 3
TT 35.7: Vortrag
Mittwoch, 16. März 2011, 15:45–16:00, HSZ 301
Ab initio modeling of Bose-Einstein condensation in Pb2V3O9 — •Alexander Tsirlin and Helge Rosner — Max Planck Institute CPfS, Dresden, Germany
We present the computational approach to the microscopic study of Bose-Einstein condensation (BEC) in quantum magnets. Using density functional theory band structure calculations, we establish the microscopic magnetic model of a BEC compound Pb2V3O9, refine the model by fitting the experimental data, and further simulate the full temperature-vs-field phase diagram. In contrast to previous theoretical descriptions based on the alternating-spin-chain model, we find that Pb2V3O9 represents an unfrustrated quasi-two-dimensional spin system of coupled spin dimers. The intradimer coupling is about 30 K, whereas the interdimer couplings are both ferro- and antiferromagnetic. The structural implementation of the model is rather non-trivial, with weaker ferromagnetic couplings along the chains of corner-sharing VO6 octahedra and stronger antiferromagnetic couplings between the structural chains. Our model leads to remarkable agreement with the available experimental data on the BEC in Pb2V3O9 and discloses the role of individual exchange couplings in this compound. While antiferromagnetic couplings alone lead to a one-dimensional spin system, the presence of ferromagnetic couplings and the two-dimensionality are essential for the BEC high-field ground state of Pb2V3O9.