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Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 5: CE: Low-dimensional Systems - Materials 1

TT 5.1: Invited Talk

Monday, March 22, 2010, 14:00–14:30, H18

Field-Induced Berezinskii-Kosterlitz-Thouless Transition in a 2d Spin-Dimer System — •Michael Lang1, Ulrich Tutsch1, Bernd Wolf1, Tonia Kretz2, Hans-Wolfram Lerner2, Matthias Wagner2, Stefan Wessel3, Tanusri Saha-Dasgupta4, Harald Jeschke5, and Roser Valenti51Phys. Institut, Univ. Frankfurt, SFB/TR49, D-60438 Frankfurt (M) — 2Inst. f. Anorg. Chemie, Univ. Frankfurt SFB/TR 49, D-60438 Frankfurt(M) — 3Inst. f. Theor. Phys. III, Univ. Stuttgart, D-70550 Stuttgart — 4S.N. Bose National Centre f. Basic Science, 700098 Kolkata, India — 5Inst. f. Theor. Phys., Univ. Frankfurt, SFB/TR49, D-60438 Frankfurt(M)

Weakly-coupled spin-1/2 dimer systems exposed to a sufficiently strong magnetic field offer exciting possibilities for studying critical phenomena under well-controlled conditions [1]. A prominent example is the Bose-Einstein condensation of magnetic triplet excitations in three dimensionally (3D)-coupled systems. Here we report on a chemically-constructed multilayer bulk magnet composed of molecule-based pairs of spin S = 1/2 dimers, where, by the application of a magnetic field, a gas of magnetic excitations is formed. Based on magnetic susceptibility measurements combined with Density Functional Theory and Quantum Monte Carlo calculations, we conclude that these excitations have a distinct 2D character and that the field-induced state, revealed at low temperatures of 39 mK, is a manifestation of the Berezinskii-Kosterlitz-Thouless topological order.

[1] T. Giamarchi et al., Nature Physics 4, 198 (2008).

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