The emergence of complexity is often tied to novel forms of collective behavior driven by strong interactions. Unconventional superconductors are archetypical examples for materials in which the competition and entwining of collective forms of behavior give rise not only to a complex phase diagram, but also to unexpected properties that have resisted all attempts of a theoretical explanation. ~ German American physicist Dirk Morr
Whereas superconductivity is of coherently-paired electrons with opposite spins and momenta, charge order involves orderliness in the arrangement of electrons and holes (electron absences) that have the same spin and momenta. Antiferromagnetism relies upon charge ordering.
Charge order and superconductivity are 2 competing pairing tendencies which cannot be simultaneously satisfied. This mutual exclusivity is on display when an antiferromagnetic material gives way to superconductivity.
In between these highly-ordered states is a transition phase which defies characterization, as it does not correspond with the Landau–Fermi liquid theory, which is the accepted model of how metallic fermions interact at low temperatures. Quantum states cannot be accounted for in this transitional gap.