Coherence and single-particle excitations in the high-temperature superconductors

摘要: The 'pseudogap' observed in the electron excitation spectrum of underdoped copper oxide superconductors has become focus considerable attention field high-temperature superconductivity. In conventional superconductors, described by 'BCS' theory, an energy gap appears at superconducting transition temperature (Tc); pseudogap, contrast, is well above Tc (ref. 1) and can be large compared to BCS gap. Here I compare energies, measured different experimental techniques, for show that these reveal existence two distinct scales: Δp Δc. first, determined either angle-resolved photoemission spectroscopy or tunnelling, single-particle energy-the (per particle) required split paired charge-carriers are second scale Andreev reflection experiments, associate it with coherence range state-the macroscopic quantum condensate charges. find that, overdoped regime, Δc converge approximately same value, as would case a superconductor where pairs form condense simultaneously. But pseudogap observed, values diverge larger than Models may provide framework understanding results involve pairing condensation temperature, might occur crossover from Bose-Einstein behaviour formation striped phases.