Dresden 2011 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe
TT: Fachverband Tiefe Temperaturen
TT 49: CE: Spin Systems and Itinerant Magnets 2
TT 49.14: Vortrag
Donnerstag, 17. März 2011, 17:45–18:00, HSZ 03
Bose-Einstein Condensation in the Han purple compound: a high field NMR study — •Steffen Krämer1, Mladen Horvatic1, Claude Berthier1, Raivo Stern2, and Tsuyoshi Kimura3 — 1Laboratoire National des Champs Magnétiques Intenses, CNRS, Grenoble, France. — 2NICPB, Tallinn, Estonia. — 3Osaka University, Osaka, Japan.
The quasi-2D, antiferromagnetic exchange coupled spin-1/2 dimer compound BaCuSi2O6 (Han purple) is considered as a prototype of the magnetic field induced Bose-Einstein Condensation (BEC) of triplet excitations on a lattice. Recently, BaCuSi2O6 has been claimed to exhibit an unusual reduction of dimensionality of the BEC from 3D to 2D when lowering the temperature, induced by frustration between adjacent planes. However, due to a structural transformation at 90 K, different intradimer exchange couplings and different gaps (ΔB/ΔA =1.16) exist in every second plane along the c axis. First Nuclear Magnetic Resonance (NMR) experiments have shown that this leads to a population of bosons in the B planes, nB, much smaller than in A planes in the field range ΔA/gµB < H < ΔB/gµB where nB = 0 is expected in a model of uncoupled planes. More recently, a better model has been presented, which takes into account both frustration and quantum fluctuations. This leads to a non-zero population nB of uncondensed bosons in the B plane, increasing quadratically with (H−Hc1), as compared to the linear dependence of nA. In our contribution we compare our new NMR results, obtained at high magnetic fields (23-27 T) and low temperatures (50 mK), to these models.