Аннотация
The mechanism of high-temperature superconductivity has not been resolved
for so long because the normal state of cuprates, which exhibits
enigmatic pseudogap phenomena, is not yet understood. We performed
careful temperature- and momentum-resolved photoemission experiments
to show that the depletion of the spectral weight in slightly underdoped
cuprate superconductor, usually called the “pseudogap,” exhibits
an unexpected nonmonotonic temperature dependence: decreases linearly
approaching T∗ at which it reveals a sharp transition but does not
vanish and starts to increase gradually again at higher temperature.
The low-temperature behavior of the pseudogap is remarkably similar
to one of the incommensurate charge ordering gap in the transition-metal
dichalcogenides, while the reopening of the gap at room temperature
fits the scenario of temperature-driven metal-insulator transition.
This observation suggests that two phenomena, the electronic instability
to density-wave formation and the entropy-driven metal-to-insulator
crossover, may coexist in the normal state of cuprates.
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