From polaronic metal to Fermi liquid: Higher-order correlations

The lightly doped Fermi Hubbard model can be understood as a polaronic metal, with rather unconventional properties especially in the poorly understood pseudogap phase. The highly doped Hubbard model, on the other hand, is belived to host a rather conventional Fermi liquid phase. The crossover from one side to the other, connecting different metallic phases, remains one of the most difficult regimes to understand theoretically in these strongly correlated systems.

In a recent collaboration with LMU / MPQ / TUM Munich and Harvard, we found new signatures of this crossover in genuine higher-order spin-charge correlation functions. We show how such correlation functions indicate the breakdown of polaronic behavior, and the onset of Fermi-liquid correlations.

In the future, at even lower temperatures, refined signatures of the cross-over are expected to become visible in these experiments. In a theoretical paper (another LMU/TUM/MPQ/Harvard collaboration) we have analyzed higher-order correlations containing four spin and one charge operators and found them to dominate over lower-order correlations in the polaronic metal. We have further shown how they can provide new insights into the microscopic nature of charge carriers, and we expect that they will provide a completely new perspective on the metallic phases in the Fermi-Hubbard model in the future.