The origin and non-quasiparticle nature of Fermi arcs in Bi2Sr2CaCu2O8+δ

A Fermi arc(1,2) is a disconnected segment of a Fermi surface observed in the pseudogap phase(3,4) of cuprate superconductors. This simple description belies the fundamental inconsistency in the physics of Fermi arcs, specifically that such segments violate the topological integrity of the band(5). Efforts to resolve this contradiction of experiment and theory have focused on connecting the ends of the Fermi arc back on itself to form a pocket, with limited and controversial success(6-9). Here we show the Fermi arc, although composed of real spectral weight, lacks the quasiparticles to be a true Fermi surface(5). To reach this conclusion we developed a new photoemission-based technique that directly probes the interplay of pair-forming and pair-breaking processes with unprecedented precision. We find the spectral weight composing the Fermi arc is shifted from the gap edge to the Fermi energy by pair-breaking processes(10). Although real, this weight does not form a true Fermi surface, because the quasiparticles, although significantly broadened, remain at the gap edge. This non-quasiparticle weight may account for much of the unexplained behaviour of the pseudogap phase of the cuprates.