Emergent scaling of spin and charge correlations at the onset of the pseudogap

What is it about?

The pseudogap is a phase of matter that emerges in certain strongly correlated materials at temperatures above the onset of superconductivity. It is marked by anomalous behavior of charge carriers (electrons) and magnetic properties, and depends sensitively on the doping level—that is, the concentration of charge carriers removed from the system. In this work, a quantum gas microscope—an ultracold-atom quantum simulator— was used to investigate how magnetic correlations evolve at the onset of the pseudogap in the Fermi–Hubbard model, a paradigmatic theoretical framework for strongly correlated materials. By probing a wide range of temperatures and doping levels, it was found that that magnetic correlations collapse onto a single universal curve when expressed in terms of a characteristic temperature scale closely related to the pseudogap temperature. Strikingly, similar universal behavior is also observed in higher-order correlations, revealing how doping modifies magnetic correlations in this regime.

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Photo by Myles Bloomfield on Unsplash

Photo by Myles Bloomfield on Unsplash

Why is it important?

On the one hand, this work underscores the importance of magnetic correlations at the onset of the pseudogap, in agreement with recent theoretical predictions. On the other hand, it demonstrates that higher-order correlations—serving as a measure of the degree of correlations between elementary constituents of the system—also play a crucial role. More broadly, this study, arising from an international collaboration between experimentalists and theorists, highlights the power of quantum simulators as a benchmark for theoretical approaches, which are notoriously challenging to assess in this class of problems.