Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 24: Symposium “Condensed Matter Phases in Ultracold Atoms”

TT 24.2: Hauptvortrag

Donnerstag, 29. März 2007, 10:00–10:30, H20

Criticality and correlations in cold atomic gases — •Michael Köhl — University of Cambridge, Department of Physics, J J Thomson Avenue, Cambridge CB3 0HE, UK — ETH Zürich, Institute of Quantum Electronics, 8093 Zürich, Switzerland

Phase transitions are among the most dramatic phenomena in nature. Minute variations in the conditions controlling a system trigger a fundamental change of its properties. In the critical regime near a second-order phase transition point the fluctuations of the order parameter are so dominant that they completely govern the behavior of the system on all length scales. Using cold atomic gases, we have directly observed critical fluctuations of the order parameter near the phase transition of Bose-Einstein condensation. From the divergence of the correlation length versus temperature we have determined its critical exponent ν. Despite our densities being nine orders of magnitude smaller and our interactions considerably weaker, we find a remarkable similarity to case of the λ-transition of Helium-4.