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

The cuprate high-temperature superconductors show two different temperature/energy scales, one associated with superconductivity and one associated with the pseudogap. Whether the pseudogap energy is associated with pairing has been one of the key questions discussed for decades. I will present our shot noise results on the cuprate Bi₂Sr₂CaCu₂O_8+δ. We find that in mesoscopic junctions, noise does not generally reflect pairing when accounting for artifacts. We thus measure - for the first time in a nodal superconductor – shot noise with scanning tunneling microscopy. Our data demonstrates that the pseudogap energy coincides with the onset of electron pairing, and is spatially heterogeneous with values reaching up to 70 meV. Our results exclude a pure local order origin of the pseudogap, link the pseudogap to Cooper pair formation, and show that the limiting factor for higher T_c in cuprates is phase coherence.