Abstract

The attractive Fermi–Hubbard model is the simplest theoretical model for studying pairing and superconductivity of fermions on a lattice. It exhibits many interesting features including a short-coherence length at intermediate coupling and a pseudogap regime with anomalous properties. Here we study an experimental realization of this model using a two-dimensional (2D) atomic Fermi gas in an optical lattice. Using a new technique for selective imaging of doublons with a quantum gas microscope, we observe chequerboard doublon density correlations in the normal state close to half-filling. With the aid of quantum Monte Carlo simulations, we show that the measured doublon density correlations allow us to put a lower bound on the strength of s-wave pairing correlations in our system. We compare the temperature sensitivity of the doublon density correlations and the paired atom fraction and find the correlations to be a much better thermometer. Accurate thermometry of attractive lattice systems will be essential in the quest for optimizing cooling schemes to reach superfluid phases in future experiments.

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Acknowledgements

This work was supported by the NSF (grant no. DMR-1607277), the David and Lucile Packard Foundation (grant no. 2016-65128), and the AFOSR Young Investigator Research Program (grant no. FA9550-16-1-0269). W.S.B. was supported by an Alfred P. Sloan Foundation fellowship. P.T.B. was supported by the DoD through the NDSEG Fellowship Program.

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  1. Department of Physics, Princeton University, Princeton, New Jersey 08544, USA

    • Debayan Mitra
    • , Peter T. Brown
    • , Elmer Guardado-Sanchez
    • , Stanimir S. Kondov
    • , Trithep Devakul
    • , David A. Huse
    • , Peter Schauß
    •  & Waseem S. Bakr

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All authors contributed extensively to the work presented in this paper.

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The authors declare no competing financial interests.

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Correspondence to Waseem S. Bakr.

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https://doi.org/10.1038/nphys4297