Spin transport in a Mott insulator of ultracold fermions
Simulating transport with cold atoms
Much can be learned about the nature of a solid from how charge and spin propagate through it. Transport experiments can also be performed in quantum simulators such as cold atom systems, in which individual atoms can be imaged using quantum microscopes. Now, two groups have investigated transport in the so-called Fermi-Hubbard model using a two-dimensional optical lattice filled with one fermionic atom per site (see the Perspective by Brantut). Moving away from half-filling to enable charge transport, Brown et al. found that the resistivity had a linear temperature dependence, not unlike that seen in the strange metal phase of cuprate superconductors. In a complementary study on spin transport, Nichols et al. observed spin diffusion driven by superexchange coupling.
Abstract
Strongly correlated materials are expected to feature unconventional transport properties, such that charge, spin, and heat conduction are potentially independent probes of the dynamics. In contrast to charge transport, the measurement of spin transport in such materials is highly challenging. We observed spin conduction and diffusion in a system of ultracold fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong interactions, spin diffusion is driven by super-exchange and doublon-hole–assisted tunneling, and strongly violates the quantum limit of charge diffusion. The technique developed in this work can be extended to finite doping, which can shed light on the complex interplay between spin and charge in the Hubbard model.
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Supplementary Material
Summary
Supplementary Text
Figs. S1 to S6
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Volume 363 | Issue 6425
25 January 2019
25 January 2019
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Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
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Submission history
Received: 26 February 2018
Accepted: 20 November 2018
Published in print: 25 January 2019
Acknowledgments
We thank W. S. Bakr, M. Greiner, and their research groups for fruitful discussions. Funding: Supported by NSF, AFOSR, an AFOSR MURI on Exotic Quantum Phases, ARO, ONR, the David and Lucile Packard Foundation, and Gordon and Betty Moore Foundation grant GBMF5279. E.K. was supported by NSF grant DMR-1609560. The computations were performed in part on the Teal computer cluster of the Department of Physics and Astronomy of San José State University and in part on the Spartan high-performance computing facility at San José State University supported by NSF grant OAC-1626645. T.S. was supported by NSF grant DMR-1608505 and partially through a Simons Investigator Award from the Simons Foundation. Author contributions: M.A.N., L.W.C., M.O., T.R.H., E.M., H.Z., and M.W.Z. planned and performed the experiment and analyzed the data. E.K. performed the NLCE simulations. All authors contributed to the interpretation of the data and the preparation of the manuscript. Competing interests: The authors declare no competing financial interests. Data and materials availability: All data shown in this work can be found in an online database (55).
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