Theoretical Nanophysics
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Direct imaging of magnetic Hubbard polarons

Joannis Koepsell, LMU

09.11.2018 at 09:00 

Polarons are among the most successful and renowned theoretical concepts to treat an overwhelming diversity of complex many-body-phenomena. Yet, a direct observation via real space correlations of such quasiparticles is lacking. Here we report the direct microscopic observation of a magnetic polaron in the doped Fermi-Hubbard model, harnessing the full single-site spin and density resolution of our ultracold-atom quantum simulator. We reveal the dressing of mobile impurities by a local reduction in antiferromagnetic order, which is caused by the competition between kinetic and magnetic energy. Using an optical tweezer to pin the position of a single dopant, we demonstrate that indeed dopant delocalization is responsible for the modification of magnetic correlations. Furthermore, we perform a comparison of the local spin environment to exact diagonalization and an effective string model at finite temperature, which predict the same polaron size as observed in the experiment on the order of one lattice site. With this work we pave the way towards microscopic studies of polaron-polaron interactions and their relation to the pseudogap and strange metal phase.

A 450, Theresienstr. 37