期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2018
卷号：115
期号：21
页码：5392-5396
DOI：10.1073/pnas.1721495115
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：A central mystery in high-temperature superconductivity is the origin of the so-called strange metal (i.e., the anomalous conductor from which superconductivity emerges at low temperature). Measuring the dynamic charge response of the copper oxides, χ ″ ( q , ω ) , would directly reveal the collective properties of the strange metal, but it has never been possible to measure this quantity with millielectronvolt resolution. Here, we present a measurement of χ ″ ( q , ω ) for a cuprate, optimally doped Bi2.1Sr1.9CaCu2O8+x ( T c = 91 K), using momentum-resolved inelastic electron scattering. In the medium energy range 0.1–2 eV relevant to the strange metal, the spectra are dominated by a featureless, temperature- and momentum-independent continuum persisting to the electronvolt energy scale. This continuum displays a simple power-law form, exhibiting q 2 behavior at low energy and q 2/ ω 2 behavior at high energy. Measurements of an overdoped crystal ( T c = 50 K) showed the emergence of a gap-like feature at low temperature, indicating deviation from power law form outside the strange-metal regime. Our study suggests the strange metal exhibits a new type of charge dynamics in which excitations are local to such a degree that space and time axes are decoupled.
关键词：non-Fermi liquid ; strange metal ; cuprates ; quantum criticality ; electron energy-loss spectroscopy
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