Аннотация
A key question in condensed-matter physics is to understand how high-temperature
superconductivity emerges on adding mobile charged carriers to an
antiferromagnetic Mott insulator. We address this question using
angle-resolved photoemission spectroscopy to probe the electronic
excitations of the non-superconducting state that exists between
the Mott insulator and the d-wave superconductor in Bi2Sr2CaCu2O8+δ.
Despite a temperature-dependent resistivity characteristic of an
insulator, the excitations in this intermediate state have a highly
anisotropic energy gap that vanishes at four points in momentum space.
This nodal-liquid state has the same gap structure as that of the
d-wave superconductor but no sharp quasiparticle peaks. We observe
a smooth evolution of the excitation spectrum, along with the appearance
of coherent quasiparticles, as one goes through the insulator-to-superconductor
transition as a function of doping. Our results suggest that high-temperature
superconductivity emerges when quantum phase coherence is established
in a non-superconducting nodal liquid.
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