[seminar] Seminar na IF-u u četvrtak 13.4.2017. u 15:00h - dr. A. Rançon, Lille

[Damir Staresinic]

Institut za fiziku, Bijenička cesta 46, 

predavaonica u zgradi Mladen Paić četvrtak, 13. travnja 2017., u 15:00 sati 
Multiple Transitions of Coupled Atom-Molecule Bosonic Mixtures in Two Dimension 
dr. A. Rançon 
Laboratoire de Physique des Lasers, Atomes et Molécules (PhLAM), Université Lille 1 


Motivated by the physics of coherently coupled, ultracold atom-molecule mixtures, we investigate a classical model possessing the same symmetry – namely a U(1)×Z2 symmetry, associated with the mass conservation in the mixture (U(1) symmetry), times the Z2 symmetry in the phase relationship between atoms and molecules. 

In two spatial dimensions the latter symmetry can lead to a finite-temperature Ising transition, associated with (quasi) phase locking between the atoms and the molecules. On the other hand, the U(1) symmetry has an associated Berezinskii-Kosterlitz-Thouless (BKT) transition towards quasi-condensation of atoms or molecules. The existence of the two transitions is found to depend crucially on the population imbalance (or detuning) between atoms and molecules: when the molecules are majority in the system, their BKT quasi-condensation transition occurs at a higher temperature than that of the atoms; the latter has the unconventional nature of an Ising (quasi) phase-locking transition, lacking a finite local order parameter below the critical temperature. When the balance is gradually biased towards the atoms, the two transitions merge together to leave out a unique BKT transition, at which both atoms and molecules acquire quasi-long-range correlations, but only atoms exhibit conventional BKT criticality, with binding of vortex-antivortex pairs into short-range dipoles. The molecular vortex-antivortex excitations bind as well, but undergo a marked crossover from a high-temperature regime in which they are weakly bound, to a low-temperature regime of strong binding, reminiscent of their transition in the absence of atom-molecule coupling. 





Voditelji seminara IF-a: [ mailto:natasav at ifs.hr | Nataša Vujičić ] i [ mailto:damirs at ifs.hr | Damir Starešinić ] 

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