Equivalence of pseudogap and pairing energy in a cuprate high-temperature superconductor

The pseudogap stands out in the phase diagram of the cuprate high-temperature superconductors because its origin and relationship to superconductivity remain elusive. The origin of the pseudogap has been debated, with competing hypotheses attributing it to preformed electron pairs or local order, such as charge density waves. We present unambiguous evidence supporting the pairing scenario, using local shot-noise spectroscopy measurements in Bi 2 Sr 2 CaCu 2 O 8+δ . Our data demonstrate that the pseudogap energy coincides with the onset of electron pairing and is spatially heterogeneous with values reaching up to 70 milli–electron volts. Our results exclude a pure local order origin of the pseudogap, link the pseudogap to Cooper pair formation, and suggest that the limiting factor for higher critical temperature in cuprates is phase coherence.