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首页> 外文期刊>Physical review >Roles of intrinsic anisotropy and π-band pairbreaking effects on critical currents in tilted-c-axis MgB_2 films probed by magneto-optical and transport measurements
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Roles of intrinsic anisotropy and π-band pairbreaking effects on critical currents in tilted-c-axis MgB_2 films probed by magneto-optical and transport measurements

机译:磁光和输运测量探测c轴倾斜MgB_2薄膜中本征各向异性和π带成对断裂对临界电流的作用

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摘要

Investigations of MgB_2 and Fe-based superconductors in recent years have revealed many unusual effects of multiband superconductivity, but manifestations of anisotropic multiband effects in the critical current density J_c have not been addressed experimentally, mostly because of the difficulties in measuring J_c along the c axis. To investigate the effect of very different intrinsic anisotropies of σ and π electron bands in MgB_2 on current transport, we grew epitaxial films with a tilted c axis (θ ~ 19.5°), which enabled us to measure the components of J_c along both the ab plane and the c axis using magneto-optical and transport techniques. These measurements were combined with scanning and transmission electron microscopy, which revealed terraced steps on the surface of the tilted-c-axis films. The measured field and temperature dependencies of the anisotropic J_c(H) show that J_(c,L) parallel to the terraced steps is higher than J_(c,T) perpendicular to the terraced steps, and J_c of thinner films (50 nm) obtained from transport experiments at 0.1 T reaches ~10% of the depairing current density J_d in the ab plane, while magneto-optical imaging revealed much higher J_c at lower fields. To analyze the experimental data we developed a model of anisotropic vortex pinning which accounts for the observed behavior of J_c in the tilted-c-axis films and suggests that the apparent anisotropy of J_c is affected by current pairbreaking effects in the weaker π band. Our results indicate that the out-of-plane current transport mediated by the π band could set the ultimate limit of J_c in MgB_2 polycrystals.
机译:近年来对MgB_2和Fe基超导体的研究揭示了多带超导的许多不同寻常的影响,但是在临界电流密度J_c中各向异性多带效应的表现尚未通过实验解决,主要是因为在沿c轴测量J_c方面存在困难。为了研究MgB_2中σ和π电子带的非常不同的固有各向异性对电流传输的影响,我们生长了倾斜c轴(θ〜19.5°)的外延膜,这使我们能够沿ab和ab测量J_c的分量。平面和c轴使用磁光和传输技术。这些测量与扫描和透射电子显微镜相结合,揭示了倾斜c轴薄膜表面的阶梯状台阶。各向异性J_c(H)的实测场和温度依赖性表明,平行于阶梯台阶的J_(c,L)大于垂直于阶梯台阶的J_(c,T),而较薄薄膜(50 nm)的J_c在0.1 T处通过传输实验获得的信号在ab平面中达到了去耦电流密度J_d的〜10%,而磁光成像显示在较低的磁场下J_c更高。为了分析实验数据,我们建立了各向异性涡旋钉扎模型,该模型解释了倾斜c轴薄膜中J_c的观察到的行为,并表明J_c的表观各向异性受弱π波段中电流成对作用的影响。我们的结果表明,π带介导的面外电流传输可以设定MgB_2多晶中J_c的极限。

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  • 来源
    《Physical review》 |2014年第21期|214509.1-214509.12|共12页
  • 作者单位

    Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA;

    Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA;

    Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA;

    Department of Physics, Old Dominion University, Norfolk, Virginia 23529, USA;

    Department of Applied Chemistry, The University of Tokyo, Tokyo 113-8656, Japan JST-PRESTO, Saitama 332-0012, Japan;

    CNR-SPIN and University of Genova, 16148 Genova, Italy;

    CNR-SPIN and University of Genova, 16148 Genova, Italy;

    Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA;

    Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA;

    Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    metals; alloys and binary compounds (including A15, MgB2, etc.); critical currents;

    机译:金属;合金和二元化合物(包括A15;MgB2等);临界电流;

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