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  • American Association for the Advancement of Science (AAAS)
  • 2015-2019  (6)
  • 1970-1974
  • 1
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    Uniaxial pressure control of competing orders in a high-temperature superconductor (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018
    Description: 〈p〉Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa〈sub〉2〈/sub〉Cu〈sub〉3〈/sub〉O〈sub〉6.67〈/sub〉 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the 〈i〉a〈/i〉 axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials.〈/p〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Nearly free electrons in a 5d delafossite oxide metal (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-10-25
    Description: Understanding the role of electron correlations in strong spin-orbit transition-metal oxides is key to the realization of numerous exotic phases including spin-orbit–assisted Mott insulators, correlated topological solids, and prospective new high-temperature superconductors. To date, most attention has been focused on the 5 d iridium-based oxides. We instead consider the Pt-based delafossite oxide PtCoO 2 . Our transport measurements, performed on single-crystal samples etched to well-defined geometries using focused ion beam techniques, yield a room temperature resistivity of only 2.1 microhm·cm (μ-cm), establishing PtCoO 2 as the most conductive oxide known. From angle-resolved photoemission and density functional theory, we show that the underlying Fermi surface is a single cylinder of nearly hexagonal cross-section, with very weak dispersion along k z . Despite being predominantly composed of d -orbital character, the conduction band is remarkably steep, with an average effective mass of only 1.14 m e . Moreover, the sharp spectral features observed in photoemission remain well defined with little additional broadening for more than 500 meV below E F , pointing to suppressed electron-electron scattering. Together, our findings establish PtCoO 2 as a model nearly-free–electron system in a 5 d delafossite transition-metal oxide.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    A single-ligand ultra-microporous MOF for precombustion CO2 capture and hydrogen purification (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-12-19
    Description: Metal organic frameworks (MOFs) built from a single small ligand typically have high stability, are rigid, and have syntheses that are often simple and easily scalable. However, they are normally ultra-microporous and do not have large surface areas amenable to gas separation applications. We report an ultra-microporous (3.5 and 4.8 Å pores) Ni-(4-pyridylcarboxylate) 2 with a cubic framework that exhibits exceptionally high CO 2 /H 2 selectivities (285 for 20:80 and 230 for 40:60 mixtures at 10 bar, 40°C) and working capacities (3.95 mmol/g), making it suitable for hydrogen purification under typical precombustion CO 2 capture conditions (1- to 10-bar pressure swing). It exhibits facile CO 2 adsorption-desorption cycling and has CO 2 self-diffusivities of ~3 x 10 –9 m 2 /s, which is two orders higher than that of zeolite 13X and comparable to other top-performing MOFs for this application. Simulations reveal a high density of binding sites that allow for favorable CO 2 -CO 2 interactions and large cooperative binding energies. Ultra-micropores generated by a small ligand ensures hydrolytic, hydrostatic stabilities, shelf life, and stability toward humid gas streams.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Uniaxial pressure control of competing orders in a high-temperature superconductor (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-11-30
    Description: Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa 2 Cu 3 O 6.67 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the a axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials.
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Evidence for hydrodynamic electron flow in PdCoO(2) (2016)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2016-02-26
    Description: Electron transport is conventionally determined by the momentum-relaxing scattering of electrons by the host solid and its excitations. Hydrodynamic fluid flow through channels, in contrast, is determined partly by the viscosity of the fluid, which is governed by momentum-conserving internal collisions. A long-standing question in the physics of solids has been whether the viscosity of the electron fluid plays an observable role in determining the resistance. We report experimental evidence that the resistance of restricted channels of the ultrapure two-dimensional metal palladium cobaltate (PdCoO2) has a large viscous contribution. Comparison with theory allows an estimate of the electronic viscosity in the range between 6 x 10(-3) kg m(-1) s(-1) and 3 x 10(-4) kg m(-1) s(-1), versus 1 x 10(-3) kg m(-1) s(-1) for water at room temperature.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Moll, Philip J W -- Kushwaha, Pallavi -- Nandi, Nabhanila -- Schmidt, Burkhard -- Mackenzie, Andrew P -- New York, N.Y. -- Science. 2016 Mar 4;351(6277):1061-4. doi: 10.1126/science.aac8385. Epub 2016 Feb 11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland. Department of Physics, University of California, Berkeley, CA 94720, USA. Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany. ; Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany. ; Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany. Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, UK. andy.mackenzie@cpfs.mpg.de.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26912359" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Photoionization in the time and frequency domain (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-11-17
    Description: Ultrafast processes in matter, such as the electron emission after light absorption, can now be studied using ultrashort light pulses of attosecond duration (10 –18 seconds) in the extreme ultraviolet spectral range. The lack of spectral resolution due to the use of short light pulses has raised issues in the interpretation of the experimental results and the comparison with theoretical calculations. We determine photoionization time delays in neon atoms over a 40–electron volt energy range with an interferometric technique combining high temporal and spectral resolution. We spectrally disentangle direct ionization from ionization with shake-up, in which a second electron is left in an excited state, and obtain excellent agreement with theoretical calculations, thereby solving a puzzle raised by 7-year-old measurements.
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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