by L. LeBlanc, ...., A. Paramekanti
We study ferromagnetism in a repulsively interacting two-component Fermi gas in a harmonic trap at zero net magnetization. Within a local density approximation, the two components phase-separate beyond a critical inter
action strength, with one species having a higher density at the trap center. The mean field release energy depends on the interaction strength and contains a sharp signature of this transition. To go beyond the local density approximation, we derive an energy functional which 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 which may be stabilized in a harmonic trapping potential. 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 implications for experiments on trapped two-component Fermi systems such as Li-6 and K-40 gases.
action strength, with one species having a higher density at the trap center. The mean field release energy depends on the interaction strength and contains a sharp signature of this transition. To go beyond the local density approximation, we derive an energy functional which 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 which may be stabilized in a harmonic trapping potential. 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 implications for experiments on trapped two-component Fermi systems such as Li-6 and K-40 gases.
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