Properties of Substrate Phonon Events in Superconducting Tunnel Junctions Induced by X-Ray Absorption
Properties of Substrate Phonon Events in Superconducting Tunnel Junctions Induced by X-Ray Absorption
复制标题
X 射线吸收引起的超导隧道结中基底声子事件的特性
DOI：
10.1143/jjap.39.1710
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发表时间：
2000
影响因子：
1.5
通讯作者：
T. Taino
中科院分区：
文献类型：
--
作者：
C. Otani;T. Ikeda;H. Kato;K. Kawai;H. Miyasaka;T. Oku;W. Ootani;H. Sato;H. Shimizu;Y. Takizawa;Hiroshi Watanabe;H. Nakagawa;H. Akoh;M. Aoyagi;T. Taino
研究了在蓝宝石衬底上制备的铌基超导隧道结（STJ）在X射线照射下产生的衬底声子谱。我们建立了一个几何模型，其中声子的收集效率与从吸收位置到STJ的立体角成正比。通过使用蒙特-卡罗模拟，我们成功地再现了由我们的测量获得的光谱的特征。模型谱与实测谱的比较表明，在结-衬底界面处的声阻抗失配和声子云的空间扩散在谱的确定中起着重要的作用。通过包括这些影响，我们表明，测量的光谱可以很好地再现通过调整只有一个自由参数，声子云的半径。我们估计，在5.9 keV X射线照射下，蓝宝石衬底的半径约为20 µm。
The spectra of substrate phonon events induced by illuminating with X-rays obtained with Nb-based superconducting tunnel junctions (STJs) fabricated on a sapphire substrate were examined. We constructed a geometrical model in which the collection efficiency of phonons is proportional to the solid angle subtended to the STJ from the position of the absorption. By using the Monte-Carlo simulation, we succeeded in fairly reproducing the features of the spectra obtained by our measurements. A comparison of the model spectra with the measured ones revealed that a mismatch of the acoustic impedance at the junction-substrate interface and the spatial spread of a phonon cloud play an important role in the determination of the spectra. By including these effects, we show that the measured spectra can be well reproduced by adjusting only one free parameter, the radius of the phonon cloud. We estimated this radius in a sapphire substrate to be ~20 µm under 5.9 keV X-ray illumination.