Abstract
Quantum degenerate Fermi gases provide a remarkable opportunity to study strongly interacting fermions. In contrast to other Fermi systems, such as superconductors, neutron stars or the quark-gluon plasma of the early Universe, these gases have low densities and their interactions can be precisely controlled over an enormous range. Previous experiments with Fermi gases have revealed condensation of fermion pairs. Although these and other studies were consistent with predictions assuming superfluidity, proof of superfluid behaviour has been elusive. Here we report observations of vortex lattices in a strongly interacting, rotating Fermi gas that provide definitive evidence for superfluidity. The interaction and therefore the pairing strength between two 6Li fermions near a Feshbach resonance can be controlled by an external magnetic field. This allows us to explore the crossover from a Bose–Einstein condensate of molecules to a Bardeen–Cooper–Schrieffer superfluid of loosely bound pairs. The crossover is associated with a new form of superfluidity that may provide insights into high-transition-temperature superconductors.
Similar content being viewed by others
References
Greiner, M., Regal, C. A. & Jin, D. S. Emergence of a molecular Bose–Einstein condensate from a Fermi gas. Nature 426, 537–540 (2003)
Jochim, S. et al. Bose-Einstein condensation of molecules. Science 302, 2101–2103 (2003)
Zwierlein, M. W. et al. Observation of Bose-Einstein condensation of molecules. Phys. Rev. Lett. 91, 250401 (2003)
Regal, C. A., Greiner, M. & Jin, D. S. Observation of resonance condensation of fermionic atom pairs. Phys. Rev. Lett. 92, 040403 (2004)
Zwierlein, M. W. et al. Condensation of pairs of fermionic atoms near a Feshbach resonance. Phys. Rev. Lett. 92, 120403 (2004)
Bartenstein, M. et al. Crossover from a molecular Bose-Einstein condensate to a degenerate Fermi gas. Phys. Rev. Lett. 92, 120401 (2004)
Bourdel, T. et al. Experimental study of the BEC-BCS crossover region in lithium 6. Phys. Rev. Lett. 93, 050401 (2004)
Kinast, J., Hemmer, S. L., Gehm, M. E., Turlapov, A. & Thomas, J. E. Evidence for superfluidity in a resonantly interacting Fermi gas. Phys. Rev. Lett. 92, 150402 (2004)
Bartenstein, M. et al. Collective excitations of a degenerate gas at the BEC-BCS crossover. Phys. Rev. Lett. 92, 203201 (2004)
Chin, C. et al. Observation of the pairing gap in a strongly interacting Fermi gas. Science 305, 1128–1130 (2004)
Kinast, J. et al. Heat capacity of a strongly-interacting Fermi gas. Science 307, 1296–1299 (2005)
Zwierlein, M. W., Schunck, C. H., Stan, C. A., Raupach, S. M. F. & Ketterle, W. Formation time of a fermion pair condensate. Phys. Rev. Lett. 94, 180401 (2005)
Eagles, D. M. Possible pairing without superconductivity at low carrier concentrations in bulk and thin-film superconducting semiconductors. Phys. Rev. 186, 456–463 (1969)
Leggett, A. J. in Modern Trends in the Theory of Condensed Matter (eds Pekalski, A. & Przystawa, J.) 13–27 (Proc. XVIth Karpacz Winter School of Theoretical Physics, Springer, Berlin, 1980)
Nozières, P. & Schmitt-Rink, S. Bose condensation in an attractive fermion gas: from weak to strong coupling superconductivity. J. Low Temp. Phys. 59, 195–211 (1985)
Huang, K. in Bose-Einstein Condensation (eds Griffin, A., Snoke, D. W. & Stringari, S.) 31–50 (Cambridge Univ. Press, Cambridge, 1995)
O'Hara, K. M., Hemmer, S. L., Gehm, M. E., Granade, S. R. & Thomas, J. E. Observation of a strongly interacting degenerate Fermi gas of atoms. Science 298, 2179–2182 (2002)
Rodriguez, M., Paraoanu, G.-S. & Törmä, P. Vortices in trapped superfluid Fermi gases. Phys. Rev. Lett. 87, 100402 (2001)
Bruun, G. M. & Viverit, L. Vortex state in superfluid trapped Fermi gases at zero temperature. Phys. Rev. A 64, 063606 (2001)
Pitaevskii, L. & Stringari, S. The quest for superfluidity in Fermi gases. Science 298, 2144–2146 (2002)
Cozzini, M. & Stringari, S. Fermi gases in slowly rotating traps: superfluid versus collisional hydrodynamics. Phys. Rev. Lett. 91, 070401 (2002)
Bulgac, A. & Yu, Y. Vortex state in a strongly coupled dilute atomic fermionic superfluid. Phys. Rev. Lett. 91, 190404 (2003)
Schecter, D. A., Dubin, D. H. E., Fine, K. S. & Driscoll, C. F. Vortex crystals from 2D Euler flow: Experiment and simulation. Phys. Fluids 11, 905–914 (1999)
Hadzibabic, Z. et al. Fifty-fold improvement in the number of quantum degenerate fermionic atoms. Phys. Rev. Lett. 91, 160401 (2003)
Dieckmann, K. et al. Decay of ultracold fermionic lithium gas near a Feshbach resonance. Phys. Rev. Lett. 89, 203201 (2002)
Bartenstein, M. et al. Precise determination of 6Li cold collision parameters by radio-frequency spectroscopy on weakly bound molecules. Phys. Rev. Lett. 94, 103201 (2004)
Matthews, M. R. et al. Vortices in a Bose-Einstein condensate. Phys. Rev. Lett. 83, 2498–2501 (1999)
Madison, K. W., Chevy, F., Wohlleben, W. & Dalibard, J. Vortex formation in a stirred Bose-Einstein condensate. Phys. Rev. Lett. 84, 806–809 (2000)
Abo-Shaeer, J. R., Raman, C., Vogels, J. M. & Ketterle, W. Observation of vortex lattices in Bose-Einstein condensates. Science 292, 476–479 (2001)
Haljan, P. C., Coddington, I., Engels, P. & Cornell, E. A. Driving Bose-Einstein-condensate vorticity with a rotating normal cloud. Phys. Rev. Lett. 87, 210403 (2001)
Hodby, E., Hechenblaikner, G., Hopkins, S. A., Maragò, O. M. & Foot, C. J. Vortex nucleation in Bose-Einstein condensates in an oblate, purely magnetic potential. Phys. Rev. Lett. 88, 010405 (2002)
Carr, L. D., Shlyapnikov, G. V. & Castin, Y. Achieving a BCS transition in an atomic Fermi gas. Phys. Rev. Lett. 92, 150404 (2004)
Onofrio, R. et al. Surface excitations in a Bose-Einstein condensate. Phys. Rev. Lett. 84, 810–813 (2000)
Anglin, J. R. Local vortex generation and the surface mode spectrum of large Bose-Einstein condensates. Phys. Rev. Lett. 87, 240401 (2001)
Madison, K. W., Chevy, F., Bretin, V. & Dalibard, J. Stationary states of a rotating Bose-Einstein condensate: routes to vortex nucleation. Phys. Rev. Lett. 86, 4443–4446 (2001)
Raman, C., Abo-Shaeer, J. R., Vogels, J. M., Xu, K. & Ketterle, W. Vortex nucleation in a stirred Bose-Einstein condensate. Phys. Rev. Lett. 87, 210402 (2001)
Madison, K. W., Chevy, F., Wohlleben, W. & Dalibard, J. Vortices in a stirred Bose-Einstein condensate. J. Mod. Opt. 47, 2715–2723 (2000)
Abo-Shaeer, J. R., Raman, C. & Ketterle, W. Formation and decay of vortex lattices in Bose-Einstein condensates at finite temperatures. Phys. Rev. Lett. 88, 070409 (2002)
Tonini, G. & Castin, Y. Formation of a vortex lattice in a rotating BCS Fermi gas. Preprint at http://arxiv.org/cond-mat/0504612 (2005).
Acknowledgements
We thank P. Zarth for experimental assistance and C. Stan for contributions in the early stages of the experiment. We also acknowledge discussions with the participants of the OCTS conference in Ohio, and thank J. Anglin, Z. Hadzibabic, D. Kleppner and A. Leanhardt for a critical reading of the manuscript. This work was supported by the NSF, ONR, ARO and NASA.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Competing interests
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
Rights and permissions
About this article
Cite this article
Zwierlein, M., Abo-Shaeer, J., Schirotzek, A. et al. Vortices and superfluidity in a strongly interacting Fermi gas. Nature 435, 1047–1051 (2005). https://doi.org/10.1038/nature03858
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1038/nature03858
- Springer Nature Limited
This article is cited by
-
Realization of a fractional quantum Hall state with ultracold atoms
Nature (2023)
-
Fermi edge singularity in neutral electron–hole system
Nature Physics (2023)
-
Ground states of attractive Bose gases near the critical rotating velocity
Calculus of Variations and Partial Differential Equations (2023)
-
Observation of vortices and vortex stripes in a dipolar condensate
Nature Physics (2022)
-
Second sound with ultracold atoms: a brief review
AAPPS Bulletin (2022)