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Triple-gap superconductivity of MgB_2-(La,Sr)MnO_3 composite

机译：MgB_2-（La，Sr）MnO_3复合材料的三间隙超导

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The interplay of superconductivity and magnetism was studied in a composite prepared from ferromagnetic half-metallic La_(0.67)Sr_(0.33)MnO_3 (LSMO) nanoparticles and the s-wave superconductor MgB_2. A few principal effects have been found. With the onset of MgB_2 superconductivity, a spectacular drop of the sample resistance was detected and complete superconductivity was observed at temperatures up to 20 K. The basic nanocomposite characteristics (critical temperature, current-voltage dependence, percolation threshold, etc.) are strongly affected by the half-metallic LSMO and, most probably, cannot be quantitatively explained within the framework of a conventional percolation scenario. Point contact (PC) spectroscopy was used to measure directly the superconducting energy coupling. For small voltage, an excess current and doubling of the PC normal-state conductance were detected. Conductance peaks corresponding to three energy gaps are clearly observed. Two of these gaps we identified as enhanced △_π and △_σ gaps originating from the MgB_2; the third gap △_(tr) is more than three times larger than the largest MgB_2 gap. The temperature behavior of △_(tr) does not follow the BCS dependence. The experimental results have a natural and qualitative explanation within the phase-coherency scenario of proximity-induced superconductivity. Specifically, at low temperature, a p-wave spin-triplet condensate with pairing energy △_(tr) is essentially sustained in LSMO but is incapable of displaying a long-range superconducting response because of a phase-disordered state. The proximity coupling to MgB_2 restores the long-range phase coherency of the superconducting state, which, in turn, enhances the superconducting state of the MgB_2.
机译：研究了铁磁性半金属La_（0.67）Sr_（0.33）MnO_3（LSMO）纳米粒子和s波超导体MgB_2制备的复合材料的超导和磁性相互作用。已发现一些主要作用。随着MgB_2超导电性的出现，在高达20 K的温度下，样品电阻出现了明显的下降，并观察到了完全的超导电性。基本的纳米复合材料特性（临界温度，电流-电压依赖性，渗流阈值等）受到严重影响。通过半金属LSMO进行分析，很可能无法在常规渗流方案的框架内进行定量解释。点接触（PC）光谱用于直接测量超导能量耦合。对于小电压，检测到过大的电流和PC正常状态电导的两倍。清晰地观察到对应于三个能隙的电导峰。我们将其中两个缺口确定为源自MgB_2的增强的△_π和△_σ缺口。第三间隙△_（tr）是最大MgB_2间隙的三倍以上。 △_（tr）的温度行为不遵循BCS依赖性。在接近感应超导的相干场景中，实验结果具有自然和定性的解释。具体地，在低温下，具有配对能量△_（tr）的p波自旋三重态冷凝物在LSMO中基本上得以维持，但是由于相无序状态而不能显示出长距离的超导响应。与MgB_2的邻近耦合恢复了超导状态的长程相干性，进而增强了MgB_2的超导状态。

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