Electrons in solids can behave independently from one another or as collective team players, whose interactions result in emergent cooperative phenomena such as magnetism, metal–insulator transitions, and unconventional superconductivity, to name a few. That team behavior happens in so-called strongly correlated materials that raise fundamental science questions, offer promising technological applications, and have given birth to a whole subfield of condensed-matter physics.

In weakly correlated materials, such as simple metals and semiconductors, electrons reside in extended orbitals and have a large kinetic energy. One can think of their quantum state in terms of independent waves that are delocalized through the solid and have an energy spectrum organized into bands. In contrast, electrons in strongly correlated materials reside in more localized orbitals; hence it is more natural to think of their quantum states in terms of correlated particles residing near the nuclei.

Strong-correlation phenomena abound not only in materials with partially...

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