Singleparticle excitations in a trapped gas of Fermi atoms in the BCSBEC crossover region
Abstract
We investigate the singleparticle properties at T=0 of a trapped superfluid gas of Fermi atoms with a Feshbach resonance. A tunable pairing interaction associated with the Feshbach resonance leads to the BCSBoseEinstein condensate (BEC) crossover, where the character of superfluidity continuously changes from the BCStype to a BEC of composite bosons. In this paper, we extend our previous work for a uniform superfluid Fermi gas [Y. Ohashi and A. Griffin, Phys. Rev. A 67, 063612 (2003)] to include the effect of a harmonic trap. We do not use the local density approximation (LDA), but directly solve the Bogoliubovde Gennes (BdG) coupled equations. While our explicit numerical solutions are for a weak (narrow) Feshbach resonance, we argue that the singleparticle BdG excitation spectrum will exhibit the same features for a strong (broad) Feshbach resonance. Using these equations, we find selfconsistent values for the spatially dependent local density n(r) as well as the composite BCS order parameter {delta}tilde(r), the latter describing both the Cooperpair and molecular condensate contributions. Using these results, we calculate the singleparticle density of states in the crossover region, and from this determine the true singleparticle energy gap (E{sub g}) of the trapped Fermi superfluid. This is associated withmore »
 Authors:

 Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305 (Japan)
 Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7 (Canada)
 Publication Date:
 OSTI Identifier:
 20718393
 Resource Type:
 Journal Article
 Journal Name:
 Physical Review. A
 Additional Journal Information:
 Journal Volume: 72; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevA.72.013601; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 10502947
 Country of Publication:
 United States
 Language:
 English
 Subject:
 74 ATOMIC AND MOLECULAR PHYSICS; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; ATOMS; BOSEEINSTEIN CONDENSATION; BOSONS; COOPER PAIRS; ENERGY GAP; EXCITATION; FERMI GAS; FERMI LEVEL; LASER RADIATION; NUMERICAL SOLUTION; ORDER PARAMETERS; PAIRING INTERACTIONS; POTENTIALS; RESONANCE; SUPERFLUIDITY; TRAPPING; TRAPS; TUNNEL EFFECT
Citation Formats
Ohashi, Y, Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, and Griffin, A. Singleparticle excitations in a trapped gas of Fermi atoms in the BCSBEC crossover region. United States: N. p., 2005.
Web. doi:10.1103/PhysRevA.72.013601.
Ohashi, Y, Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, & Griffin, A. Singleparticle excitations in a trapped gas of Fermi atoms in the BCSBEC crossover region. United States. https://doi.org/10.1103/PhysRevA.72.013601
Ohashi, Y, Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, and Griffin, A. Fri .
"Singleparticle excitations in a trapped gas of Fermi atoms in the BCSBEC crossover region". United States. https://doi.org/10.1103/PhysRevA.72.013601.
@article{osti_20718393,
title = {Singleparticle excitations in a trapped gas of Fermi atoms in the BCSBEC crossover region},
author = {Ohashi, Y and Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7 and Griffin, A},
abstractNote = {We investigate the singleparticle properties at T=0 of a trapped superfluid gas of Fermi atoms with a Feshbach resonance. A tunable pairing interaction associated with the Feshbach resonance leads to the BCSBoseEinstein condensate (BEC) crossover, where the character of superfluidity continuously changes from the BCStype to a BEC of composite bosons. In this paper, we extend our previous work for a uniform superfluid Fermi gas [Y. Ohashi and A. Griffin, Phys. Rev. A 67, 063612 (2003)] to include the effect of a harmonic trap. We do not use the local density approximation (LDA), but directly solve the Bogoliubovde Gennes (BdG) coupled equations. While our explicit numerical solutions are for a weak (narrow) Feshbach resonance, we argue that the singleparticle BdG excitation spectrum will exhibit the same features for a strong (broad) Feshbach resonance. Using these equations, we find selfconsistent values for the spatially dependent local density n(r) as well as the composite BCS order parameter {delta}tilde(r), the latter describing both the Cooperpair and molecular condensate contributions. Using these results, we calculate the singleparticle density of states in the crossover region, and from this determine the true singleparticle energy gap (E{sub g}) of the trapped Fermi superfluid. This is associated with the ingap (or Andreev) states in the lowdensity region at the edge of the trap. We calculate the laserinduced tunneling current I({omega}) into another hyperfine state, as measured in recent rf spectroscopy experiments. This rf spectrum gives a direct probe of the quasiparticle spectrum. We show how the highenergy part of I({omega}) gives information about {delta}tilde(r=0) at the center of the trap (which is comparable to the Fermi energy {epsilon}{sub F} in the crossover region). We show that I({omega}) is very dependent on the spatial profile of the pair potential {delta}tilde(r) that is used. We also emphasize that the narrow 'unpaired atom peak in the rf data gives information about E{sub g} and the lowenergy (<<{epsilon}{sub F}) ingap states of a Fermi superfluid. While our calculations are limited to T=0, we use them to discuss the recent data of Chin et al. and the LDA calculations of Toermae and coworkers. The LDA, while useful, can lead to an incorrect physical picture of the lowdensity surface region of the Fermi superfluid.},
doi = {10.1103/PhysRevA.72.013601},
url = {https://www.osti.gov/biblio/20718393},
journal = {Physical Review. A},
issn = {10502947},
number = 1,
volume = 72,
place = {United States},
year = {2005},
month = {7}
}