Universal Spin Transport in a Strongly Interacting Fermi Gas
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Author(s)
Sommer, Ariel Tjodolv
Roati, Giacomo
Zwierlein, Martin Wolfram
Ku, Mark J. H.
Date Issued
April 2011
Journal
Nature
Publisher
Nature Publishing Group
Citation
Sommer, Ariel et al. “Universal spin transport in a strongly interacting Fermi gas.” Nature 472.7342 (2011): 201-204.
Version
Author's final manuscript
Abstract
Transport of fermions is central in many elds of physics. Electron transport runs modern technology,
de ning states of matter such as superconductors and insulators, and electron spin, rather
than charge, is being explored as a new carrier of information [1]. Neutrino transport energizes
supernova explosions following the collapse of a dying star [2], and hydrodynamic transport of the
quark-gluon plasma governed the expansion of the early Universe [3]. However, our understanding
of non-equilibrium dynamics in such strongly interacting fermionic matter is still limited. Ultracold
gases of fermionic atoms realize a pristine model for such systems and can be studied in real time
with the precision of atomic physics [4, 5]. It has been established that even above the super
uid
transition such gases
ow as an almost perfect
uid with very low viscosity [3, 6] when interactions
are tuned to a scattering resonance. However, here we show that spin currents, as opposed to
mass currents, are maximally damped, and that interactions can be strong enough to reverse spin
currents, with opposite spin components reflecting off each other. We determine the spin drag coefficient, the spin di usivity, and the spin susceptibility, as a function of temperature on resonance and
show that they obey universal laws at high temperatures. At low temperatures, the spin di usivity
approaches a minimum value set by ħ/m, the quantum limit of di usion, where ħ is the reduced
Planck's constant and m the atomic mass. For repulsive interactions, our measurements appear to
exclude a metastable ferromagnetic state [7{9].
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Research Laboratory of Electronics
MIT-Harvard Center for Ultracold Atoms
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DOI of Published Version
https://doi.org/10.1038/nature09989
