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Incoherent strange metal sharply bounded by a critical doping in Bi2212

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Science  29 Nov 2019:
Vol. 366, Issue 6469, pp. 1099-1102
DOI: 10.1126/science.aaw8850

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A sharp boundary in the cuprates

Many physicists working on cuprate superconductors believe that the so-called strange metal phase in the cuprate phase diagram is associated with a quantum critical point. Within this picture, the quantum critical point gives rise to a V-shaped region in the doping-temperature phase diagram of the cuprates: the strange metal phase. Chen et al. used angle-resolved photoemission spectroscopy in the cuprate family Bi2212 to challenge this view. By taking comprehensive measurements as a function of doping and temperature—and making sure that the signal was not affected by environmental conditions—they found an incoherent strange metal phase that was sharply separated from a conventional phase by a temperature-independent vertical line in the phase diagram.

Science, this issue p. 1099

Abstract

In normal metals, macroscopic properties are understood using the concept of quasiparticles. In the cuprate high-temperature superconductors, the metallic state above the highest transition temperature is anomalous and is known as the “strange metal.” We studied this state using angle-resolved photoemission spectroscopy. With increasing doping across a temperature-independent critical value pc ~ 0.19, we observed that near the Brillouin zone boundary, the strange metal, characterized by an incoherent spectral function, abruptly reconstructs into a more conventional metal with quasiparticles. Above the temperature of superconducting fluctuations, we found that the pseudogap also discontinuously collapses at the very same value of pc. These observations suggest that the incoherent strange metal is a distinct state and a prerequisite for the pseudogap; such findings are incompatible with existing pseudogap quantum critical point scenarios.

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