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The origin of the anomalous superconducting properties of MgB_2

机译：MgB_2异常超导性质的起源

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Magnesium diboride1 differs from ordinary metallic superconductors in several important ways, including the failure of conventional models to predict accurately its unusually high transition temperature, the effects of isotope substitution on the critical transition temperature, and its anomalous specific heat. A detailed examination of the energy associated with the formation of charge-carrying pairs, referred to as the 'superconducting energy gap', should clarify why MgB_2 is different. Some early experimental studies have indicated that MgB_2 has multiple gaps, but past theoretical studies have not explained from first principles the origin of these gaps and their effects. Here we report an ab initio calculation of the superconducting gaps in MgB_2 and their effects on measurable quantities. An important feature is that the electronic states dominated by orbitals in the boron plane couple strongly to specific phonon modes, making pair formation favourable. This explains the high transition temperature, the anomalous structure in the specific heat, and the existence of multiple gaps in this material. Our analysis suggests comparable or higher transition temperatures may result in layered materials based on B, C and N with partially filled planar orbitals.
机译：二硼化镁在几个重要方面与普通金属超导体不同，包括常规模型无法准确预测其异常高的转变温度，同位素替代对临界转变温度的影响以及其比热异常。与载流子对的形成有关的能量的详细检查，称为“超导能隙”，应阐明为什么MgB_2不同。一些早期的实验研究表明，MgB_2具有多个缺口，但是过去的理论研究并未从第一原理中解释这些缺口的起源及其作用。在这里，我们报告了从头算计算MgB_2中的超导间隙及其对可测量量的影响。一个重要的特征是，硼平面中由轨道支配的电子态与特定的声子模强耦合，从而有利于成对形成。这解释了较高的转变温度，比热中的异常结构以及这种材料中存在多个间隙。我们的分析表明，相当或更高的转变温度可能会导致基于B，C和N的层状材料具有部分填充的平面轨道。

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