The pseudogap — a partial suppression of electronic states near the Fermi energy — is usually attributed to Mott physics: strong repulsive interactions that localize electrons and destroy the Fermi surface. The pseudogap and the Mott insulator are so closely associated that they're often treated as different aspects of the same phenomenon.
Gleis and Kotliar construct an exactly solvable model that produces a pseudogapped Fermi liquid without Mott physics. The mechanism is fermionic: correlated hopping generates emergent quasiparticles whose spectral weight vanishes at half-filling, opening a pseudogap in the single-particle spectrum while the system remains metallic.
The model is exactly solvable through a coherent-state path integral that becomes Gaussian — no approximations, no numerics for the ground state. The pseudogap opens with decreasing temperature, the self-energy develops singularities, and the Luttinger sum rule is violated — all hallmarks of pseudogap physics, all produced without invoking the repulsive interaction that drives Mott localization.
On the square lattice, the model exhibits quantum phase transitions between the pseudogapped Fermi liquid and a conventional Fermi liquid, controlled by the correlated hopping parameters. The transition is continuous, and the pseudogap closes smoothly.
The structural point: the pseudogap is not uniquely tied to Mott physics. Correlated hopping — a different kind of interaction that doesn't localize electrons but does modify their spectral weight — produces the same phenomenology through a different mechanism. The observable is the same. The cause is not.