Pair condensation of polarized fermions in the BCS-BEC crossover

Year: 2014

Authors: Bighin G., Mazzarella G., Dell’Anna L., Salasnich L.

Autors Affiliation: Dipartimento di Fisica e Astronomia ‘Galileo Galilei’, Università di Padova, Via Marzolo 8, I-35131 Padova, Italy;
Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova, Via Marzolo 8, I-35131 Padova, Italy;
Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (CNISM), Unità di Padova, Via Marzolo 8, I-35131 Padova, Italy;
Istituto Nazionale di Ottica (INO) del Consiglio Nazionale delle Ricerche (CNR), Sezione di Sesto Fiorentino, Via Nello Carrara, I-1-50019 Sesto Fiorentino, Italy

Abstract: We investigate a two-component Fermi gas with unequal spin populations along the BCS-BEC crossover. By using the extended BCS equations and the concept of off-diagonal-long-range-order we derive a formula for the condensate number of Cooper pairs as a function of energy gap, average chemical potential, imbalance chemical potential and temperature. Then we study the zero-temperature condensate fraction of Cooper pairs by varying interaction strength and polarization, finding a depletion of the condensate fraction by increasing the population imbalance. We also consider explicitly the presence of an external harmonic confinement and we study, within the local-density approximation, the phase separation between superfluid (SF) and normal phase regions of the polarized fermionic cloud. In particular, we calculate both condensate density profiles and total density profiles from the inner SF core to the normal region passing for the interface, where a finite jump in the density is a clear manifestation of this phase-separated regime. Finally, we compare our theoretical results with the available experimental data on the condensate fraction of polarized Li-6 atoms (Zwierlein et al 2006 Science 311 492). These experimental data are in reasonable agreement with our predictions in a suitable range of polarizations, but only in the BCS side of the crossover up to unitarity.

Journal/Review: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS

Volume: 47 (19)      Pages from: 195302-1  to: 195302-7

More Information: We thank J Tempere, N Manini, and F Toigo for fruitful discussions and suggestions. GB acknowledges financial support from Italian INFN (Istituto Nazionale di Fisica Nucleare). LD acknowledges financial support also from MIUR (FIRB 2012, Grant No. RBFR12NLNA-002). The authors acknowledge for partial support Universita di Padova (grant No. CPDA118083), Cariparo Foundation (Eccellenza grant 2011/2012), and MIUR (PRIN grant No. 2010LLKJBX).
KeyWords: BCS-BEC crossover; Fermi gases; condensation
DOI: 10.1088/0953-4075/47/19/195302

Citations: 3
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