欠掺杂和过掺杂Ba $_{x}$ K $_{1-x}$ BiO $_{3}$钙钛矿氧化物的超导性能
Superconducting properties of under- and over-doped Ba$_{x}$K$_{1-x}$BiO$_{3}$ perovskite oxide
摘要：
在本研究中，我们研究的Ba $_{x}$ K $_{1-x}$ BiO $_{3}$（BKBO）超导体在下（$x=0.5$）和过掺杂（$x=0.7$）制度的热力学性质，在Migdal-Eliashberg形式主义的框架内。分析结果表明，该化合物中超导相的产生是电子-声子配对机制的结果。特别是，我们表明，BKBO的特点是由相对较高的临界值的库仑赝势，这与掺杂水平的变化，并不遵循Morel-Anderson模型。在下文中，估计相应的超导带隙尺寸和相关的无量纲比随着掺杂而增加，与实验预测一致。此外，电子的有效质量被发现采取在整个掺杂和温度区域的高值。最后，超导带隙的特征无量纲比率，临界磁场和超导态的比热被预测为超过Bardeen-Cooper-Schrieffer理论中设定的限制，这表明强耦合和延迟效应在分析的化合物中的关键作用。提出的结果补充了我们以前的调查和帐户的强耦合声子介导的字符在BKBO超导相在任何掺杂水平。
英文摘要：
In the present study, we investigate the thermodynamic properties of the Ba$_{x}$K$_{1-x}$BiO$_{3}$ (BKBO) superconductor in the under- ($x=0.5$) and over-doped ($x=0.7$) regime, within the framework of the Migdal-Eliashberg formalism. The analysis is conducted to verify that the electron-phonon pairing mechanism is responsible for the induction of the superconducting phase in the mentioned compound. In particular, we show that BKBO is characterized by the relatively high critical value of the Coulomb pseudopotential, which changes with doping level and does not follow the Morel-Anderson model. In what follows, the corresponding superconducting band gap size and related dimensionless ratio are estimated to increase with the doping, in agreement with the experimental predictions. Moreover the effective mass of electrons is found to take on high values in the entire doping and temperature region. Finally, the characteristic dimensionless ratios for the superconducting band gap, the critical magnetic field and the specific heat for the superconducting state are predicted to exceed the limits set within the Bardeen-Cooper-Schrieffer theory, suggesting pivotal role of the strong-coupling and retardation effects in the analyzed compound. Presented results supplement our previous investigations and account for the strong-coupling phonon-mediated character of the superconducting phase in BKBO at any doping level.
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