April 06 2015

13.04. - 14.04.2015: Visit of Laurent de Forges de Parny

Laurent de Forges de Parny (ENS Lyon) is visiting us and will give a talk in our group seminar about: "Multiple Transitions in a Coupled Atom-Molecule Mixture".

Since the pioneering experiments in 2002 by M. Greiner et al., ultracold bosons in optical lattices are ideal test bed for many condensed matter models. As you know, the Bose-Einstein condensation of pairs of particles is central in the theory of superconductivity and the control of such a mechanism is still a big challenge. Feshbach resonances - namely resonances between an unbound two-body state (atomic state) and a bound (molecular) state - allow the conversion of two unbound atoms into a molecule and vice versa.

My numerical studies focus on a 2D mixture of interacting bosonic atoms and molecules with conversion between these two species. This system involves many interesting phases and phase transitions:
- At zero temperature, the system exhibits molecular and atomic-molecular condensates and an insulating phase stabilized by the conversions - a "Feshbach insulator". First order, 3D XY and 3D Ising transitions appear.
- At finite temperature, this system also reveals interesting transitions: when increasing the temperature, the system evolves from an atomic-molecular superfluid to a molecular superfluid and then to a normal Bose liquid. The multiple transitions involved (2D Ising and KT transitions) are very well described by a coupled XY model and scaling analysis.

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