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Luciuk C, Smale S, Böttcher F, Sharum H, Olsen BA, Trotzky S, Enss T, Thywissen JH. Observation of Quantum-Limited Spin Transport in Strongly Interacting Two-Dimensional Fermi Gases. Phys Rev Lett 2017; 118:130405. [PMID: 28409948 DOI: 10.1103/physrevlett.118.130405] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Indexed: 06/07/2023]
Abstract
We measure the transport properties of two-dimensional ultracold Fermi gases during transverse demagnetization in a magnetic field gradient. Using a phase-coherent spin-echo sequence, we are able to distinguish bare spin diffusion from the Leggett-Rice effect, in which demagnetization is slowed by the precession of a spin current around the local magnetization. When the two-dimensional scattering length is tuned to be comparable to the inverse Fermi wave vector k_{F}^{-1}, we find that the bare transverse spin diffusivity reaches a minimum of 1.7(6)ℏ/m, where m is the bare particle mass. The rate of demagnetization is also reflected in the growth rate of the s-wave contact, observed using time-resolved spectroscopy. The contact rises to 0.28(3)k_{F}^{2} per particle, which quantifies how scaling symmetry is broken by near-resonant interactions, unlike in unitary three-dimensional systems. Our observations support the conjecture that, in systems with strong scattering, the local relaxation rate is bounded from above by k_{B}T/ℏ.
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Affiliation(s)
- C Luciuk
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - S Smale
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - F Böttcher
- 5. Physikalisches Institut and Centre for Integrated Quantum Science and Technology, Universität Stuttgart, D-70569 Stuttgart, Germany
| | - H Sharum
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - B A Olsen
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - S Trotzky
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - T Enss
- Institut für Theoretische Physik, Universität Heidelberg, D-69120 Heidelberg, Germany
| | - J H Thywissen
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
- Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
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Trotzky S, Beattie S, Luciuk C, Smale S, Bardon AB, Enss T, Taylor E, Zhang S, Thywissen JH. Observation of the Leggett-Rice effect in a unitary Fermi gas. Phys Rev Lett 2015; 114:015301. [PMID: 25615476 DOI: 10.1103/physrevlett.114.015301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Indexed: 06/04/2023]
Abstract
We observe that the diffusive spin current in a strongly interacting degenerate Fermi gas of (40)K precesses about the local magnetization. As predicted by Leggett and Rice, precession is observed both in the Ramsey phase of a spin-echo sequence, and in the nonlinearity of the magnetization decay. At unitarity, we measure a Leggett-Rice parameter γ=1.08(9) and a bare transverse spin diffusivity D(0)(⊥)=2.3(4)ℏ/m for a normal-state gas initialized with full polarization and at one-fifth of the Fermi temperature, where m is the atomic mass. One might expect γ=0 at unitarity, where two-body scattering is purely dissipative. We observe γ→0 as temperature is increased towards the Fermi temperature, consistent with calculations that show the degenerate Fermi sea restores a nonzero γ. Tuning the scattering length a, we find that a sign change in γ occurs in the range 0<(k(F)a)(-1)≲1.3, where k(F) is the Fermi momentum. We discuss how γ reveals the effective interaction strength of the gas, such that the sign change in γ indicates a switching of branch between a repulsive and an attractive Fermi gas.
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Affiliation(s)
- S Trotzky
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - S Beattie
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - C Luciuk
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - S Smale
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - A B Bardon
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
| | - T Enss
- Institut für Theoretische Physik, Universität Heidelberg, 69120 Heidelberg, Germany
| | - E Taylor
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - S Zhang
- Department of Physics, Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | - J H Thywissen
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada and Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
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Bardon AB, Beattie S, Luciuk C, Cairncross W, Fine D, Cheng NS, Edge GJA, Taylor E, Zhang S, Trotzky S, Thywissen JH. Transverse Demagnetization Dynamics of a Unitary Fermi Gas. Science 2014; 344:722-4. [DOI: 10.1126/science.1247425] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- A. B. Bardon
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - S. Beattie
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - C. Luciuk
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - W. Cairncross
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - D. Fine
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - N. S. Cheng
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - G. J. A. Edge
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - E. Taylor
- Department of Physics and Astronomy, McMaster University, L8S 4M1 Canada
| | - S. Zhang
- Department of Physics, Center of Theoretical and Computational Physics, University of Hong Kong, China
| | - S. Trotzky
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - J. H. Thywissen
- Department of Physics, University of Toronto, M5S 1A7 Canada
- Canadian Institute for Advanced Research, Toronto, Ontario, M5G 1Z8 Canada
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