نویسندگان

چکیده

  ما بررسیهای سیستماتیک خواص ابررسانایی مغناطیسی را در مواد ابررسانای جدید (NS) گزارش می‌کنیم: در ابررساناهای دمای بالای جدید (HTS) ، ابررساناهای آلی (OS) ، فولرین، نانولوله‌های کربنی، MgB2 و غیره نشان می‌دهیم که برخلاف ابررساناهای متعارف که در آن حالت ابررسانایی می‌تواند در طول چندین ده کیلومتر همدوس باشد، حدود طول همدوسی ماکروسکوپی lc در NS غالباً به کوچکی 0 /1 تا 1 0 است. در نتیجه، خواص مغناطیسی تحت تأثیر اثرات دانه‌ای–مانند و زوج شدگی جوزفسون میان-دانه‌‌ای قرار دارد. در این جا به‌طور خاص بر روی سرامیکهای HTS ابررساناهای آلی متمرکز می‌شویم. در مورد اول سه رژیم مجزا را مشاهده می‌کنیم: (i) در میدانهای خیلی کوچک (مثلاً H

کلیدواژه‌ها

عنوان مقاله [English]

Signatures of granular superconductivity and Josephson effects in macroscopic measurements: the case of new superconductors

نویسندگان [English]

  • S Senoussi
  • F Pesty

چکیده [English]

  We report systematic investigations of the magnetic superconducting properties of the new superconducting materials (NS): New high temperature superconductors (HTS), Organic superconductors (OS), fullerenes, carbon nanotubes, MgB2 etc. We show that, contrary to conventional superconductors where the superconducting state can be coherent over several tenths of km, the macroscopic coherence range lc of the NS is often as short as 0.1 to 10 µm typically. As a consequence, the magnetic properties are dominated by granular-like effects as well as Josephson coupling between grains. Here, we concentrate on HTS ceramics and organic superconductors exclusively. In the first case we observe three distinct regimes: (i) At very low field (H < 5 Oe to say) all the grains are coupled via Josephson effect and lc can be considered as infinite. (2) At intermediate field (5 < H < 50 Oe, typically) the grains are gradually decoupled by H and/or T. (iii) At higher fields all the grains are decoupled and lc roughly coincides with the diameter of the metallurgical grains. The case of OS is more subtle and is connected with a kind of order-disorder transition that occurs in most of them. For instance, in this study, we exploit quenched disorder (after crossing such a transition) in the -(BEDT-TTF)2Cu[N(CN)2]Br layered organic superconductor to get new insights on both the superconducting state (T £ 11.6 K) and the glassy transition at Tg, by studying the superconducting properties as functions of annealing time and annealing temperature around the glassy transition. Our main result is that the data can be described by a percolation molecular cluster model in which the topology and the growth of the molecular clusters obey an Ising spin-glass-like model with Tg ≈ 80 K for the hydrogenated compound and Tg ≈ 55 K for the fully deuterated one.

کلیدواژه‌ها [English]

  • critical current
  • granular superconductivity
  • organic superconductors
  • glassy transition
  • streched expoenential
  • BEDT-TTF

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