Atypical BCS-BEC crossover induced by quantum-size effects

Titelangaben

Shanenko, A. A. ; Croitoru, Mikhail D. ; Vagov, Alexei ; Axt, Vollrath Martin ; Perali, A. ; Peeters, F. M.:
Atypical BCS-BEC crossover induced by quantum-size effects.
In: Physical Review A. Bd. 86 (2012) Heft 3 . - 033612.
ISSN 1094-1622
DOI: https://doi.org/10.1103/PhysRevA.86.033612

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Abstract

Quantum-size oscillations of the basic physical characteristics of a confined fermionic condensate are a well-known phenomenon. Its conventional understanding is based on the single-particle physics, whereby the oscillations follow variations in the single-particle density of states driven by the size quantization. Here we present a study of a cigar-shaped ultracold superfluid Fermi gas, which demonstrates an important many-body aspect of the quantum-size coherent effects, overlooked previously. The many-body physics is revealed here in the atypical crossover from the Bardeen-Cooper-Schrieffer (BCS) superfluid to the Bose-Einstein condensate (BEC) induced by the size quantization of the particle motion. The single-particle energy spectrum for the transverse dimensions is tightly bound, whereas for the longitudinal direction it resembles a quasi-free dispersion. This results in the formation of a series of single-particle subbands (shells) so that the aggregate fermionic condensate becomes a coherent mixture of subband condensates. Each time when the lower edge of a subband crosses the chemical potential, the BCS-BEC crossover is approached in this subband, and the aggregate condensate contains both BCS and BEC-like components.