The local spectra remain qualitatively the same across the insulator-to-superconductor transition, and the quasiparticle interference becomes long-ranged. Each chequerboard plaquette contains approximately two holes and exhibits a stripy internal structure that has a strong influence on the superconducting spectroscopic features. We observe a smooth crossover from the Mott insulator to superconductor on small islands that have chequerboard order. We make these observations via scanning tunnelling microscopy on underdoped Bi 2La xSr 2 − xCuO 6 + δ. Here we examine the evolution of pairing and phase-ordering in underdoped cuprates, and find that a chequerboard plaquette pattern of charge order plays a crucial role, such that the global phase coherence is established once its spatial occupation exceeds a threshold. It has been proposed that pairing and phase coherence may occur separately in cuprates, and that the measured critical temperature corresponds to the phase-coherence temperature controlled by the superfluid density. The cuprate high-temperature superconductors belong to a different category because, being doped Mott insulators, they are known to have low superfluid density and are therefore susceptible to phase fluctuations. Publications of Yayu Wang Group: 'The emergence of global phase coherence from local pairing in underdoped cuprates. In conventional metallic superconductors such as aluminium, the large number of weakly bounded Cooper pairs become phase-coherent as soon as they start to form.
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