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Science 18 September 2009:
Vol. 325. no. 5947, pp. 1521 - 1524
DOI: 10.1126/science.1177112
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Reports

Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms

Gyu-Boong Jo,1,* Ye-Ryoung Lee,1 Jae-Hoon Choi,1 Caleb A. Christensen,1 Tony H. Kim,1 Joseph H. Thywissen,2 David E. Pritchard,1 Wolfgang Ketterle1

Can a gas of spin-up and spin-down fermions become ferromagnetic because of repulsive interactions? We addressed this question, for which there is not yet a definitive theoretical answer, in an experiment with an ultracold two-component Fermi gas. The observation of nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions provides strong evidence for a phase transition to a ferromagnetic state. Our observations imply that itinerant ferromagnetism of delocalized fermions is possible without lattice and band structure, and our data validate the most basic model for ferromagnetism introduced by Stoner.

1 Massachusetts Institute of Technology–Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2 Department of Physics, University of Toronto, Toronto, Ontario M5S1A7, Canada.

* To whom correspondence should be addressed. E-mail: gyuboong{at}mit.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Itinerant Ferromagnetism with Ultracold Atoms.
W. Zwerger (2009)
Science 325, 1507-1509
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