The pseudogap in cuprate superconductors — a suppression of electronic states near the Fermi level above the superconducting transition — has resisted a single explanation for decades. It looks like a gap but isn't associated with any broken symmetry in the conventional sense. One idea: the electrons fractionalize, splitting into separately trackable components that carry different quantum numbers.
Müller-Groeling et al. (arXiv:2603.13071) implement this idea for stripe order in the two-dimensional Hubbard model using SU(2) gauge theory. Electrons split into chargons (fermionic, carrying pseudospin and charge) and spinons (bosonic, carrying spin). The chargons see a mean field with stripe order — spatial modulation of charge density. The spinons fluctuate according to a nonlinear sigma model. The gauge field glues the two sectors together.
The result: a charge-ordered pseudogap phase with a reconstructed Fermi surface and a spin gap. Fermi arcs appear — disconnected segments of Fermi surface rather than a complete contour — but never exclusively near the Brillouin zone diagonals. This is diagnostic: it distinguishes the stripe-fluctuation mechanism from competing explanations (like d-density wave order) that predict arcs centered on the zone diagonals.
The fractionalization is not a mathematical trick but a physical claim: the electrons in the pseudogap state are not well-defined quasiparticles. They've split into components that propagate independently through different effective environments. The charge sector sees stripes; the spin sector sees a fluctuating landscape. What the experiment measures — the spectral function — is the recombination of these two sectors, and the arcs are where the recombination is constructive.