Repulsive Fermi gas in a harmonic trap: Ferromagnetism and spin textures

L. J. LeBlanc, J. H. Thywissen, A. A. Burkov, and A. Paramekanti
Phys. Rev. A 80, 013607 – Published 13 July 2009

Abstract

We study ferromagnetism in a repulsively interacting two-component Fermi gas in a harmonic trap. Within a local density approximation, the two components phase separate beyond a critical interaction strength, with one species having a higher density at the trap center. We discuss several easily observable experimental signatures of this transition. The mean-field release energy, its separate kinetic and interaction contributions, as well as the potential energy all depend on the interaction strength and contain a sharp signature of this transition. In addition, the conversion rate of atoms to molecules, arising from three-body collisions, peaks at an interaction strength just beyond the ferromagnetic transition point. We then go beyond the local density approximation and derive an energy functional that includes a term that depends on the local magnetization gradient and acts as a “surface tension.” Using this energy functional, we numerically study the energetics of some candidate spin textures that may be stabilized in a harmonic trapping potential at zero net magnetization. We find that a hedgehog state has a lower energy than an “in-out” domain-wall state in an isotropic trap. Upon inclusion of trap anisotropy we find that the hedgehog magnetization profile gets distorted due to the surface tension term, this distortion being more apparent for small atom numbers. We estimate that the magnetic dipole interaction does not play a significant role in this system. We consider possible implications for experiments on trapped L6i and K40 gases.

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  • Received 31 March 2009

DOI:https://doi.org/10.1103/PhysRevA.80.013607

©2009 American Physical Society

Authors & Affiliations

L. J. LeBlanc1, J. H. Thywissen1, A. A. Burkov2, and A. Paramekanti1

  • 1Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7
  • 2Department of Physics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

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Vol. 80, Iss. 1 — July 2009

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