Universality in phase transitions for ultracold fermionic atoms

Journal Article · Wed Mar 15 00:00:00 EST 2006 · Physical Review. A

DOI:https://doi.org/10.1103/PHYSREVA.73.0· OSTI ID:20786973

Diehl, S; Wetterich, C ^[1]

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1. Institut fuer Theoretische Physik, Philosophenweg 16, 69120 Heidelberg (Germany)

We describe the gas of ultracold fermionic atoms by a functional integral for atom and molecule fields. The crossover from Bose-Einstein condensation (BEC) to BCS-type superfluidity shows universal features in terms of a concentration parameter for the ratio between scattering length and average interatomic distance. We discuss the relevance of the Yukawa coupling between atoms and molecules, establish an exact narrow resonance limit, and show that renormalized quantities are independent of the Yukawa coupling for the broad resonance and BCS and BEC limits. Within our functional integral formalism we compute the atom scattering in vacuum and the molecular binding energy. This connects the universal concentration parameter to the magnetic field of a given experiment. Beyond mean-field theory we include the fluctuations of the molecule field and the renormalization effects for the atom-molecule coupling. We find excellent agreement with the observed fraction of bare molecules in {sup 6}Li and qualitative agreement with the condensate fraction in {sup 6}Li and {sup 40}K. In addition to the phase diagram and condensate fraction we compute the correlation length for molecules, the in-medium scattering length for molecules and atoms, and the sound velocity.

• OSTI ID: 20786973
• Journal Information: Physical Review. A, Vol. 73, Issue 3; Other Information: DOI: 10.1103/PhysRevA.73.033615; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1050-2947
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ATOMS
BINDING ENERGY
BOSE-EINSTEIN CONDENSATION
CORRELATIONS
COUPLING
FERMIONS
FLUCTUATIONS
INTERATOMIC DISTANCES
LITHIUM 6
MAGNETIC FIELDS
MEAN-FIELD THEORY
MOLECULES
PHASE DIAGRAMS
PHASE TRANSFORMATIONS
POTASSIUM 40
RENORMALIZATION
RESONANCE
SCATTERING
SCATTERING LENGTHS
SOUND WAVES
SUPERFLUIDITY
YUKAWA POTENTIAL