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美国研究人员发现描述超导材料性质数学公式

超导体,成长吧啊,www.czbaa.com,数学

美国麻省理工大学(MIT)研究人员发现,在超导材料的厚度、温度和电阻之间满足一种新的数学关系:材料的超导性与薄膜厚度、临界温度和薄膜电阻成比例。所有超导体中都存在这种关系。这一发现揭示了超导的性质,有望带来设计更好的超导线路,用在量子计算和超低能耗计算中。相关论文发表在最近的《物理评论快报B辑》上。

据物理学家组织网近日报道,“利用这一知识,我们能造出比以往更大面积的设备,产量也会显著提高。”论文第一作者、MIT电子设备研究实验室博士后亚钦·伊夫里说,“薄膜让人们更接近‘从超导到绝缘’的转变。超导是取决于电子集体行为的一种现象,只要让材料越来越小,就能开启这种集体行为。”

伊夫里专门研究氮化铌薄膜。氮化铌是一种热门超导材料,因为从它的“体形”来看,它的“临界温度”相对较高。临界温度是从普通金属变为超导体的转折点。但像大多数超导体一样,把它沉淀在纳米设备上作为薄膜时,临界温度更低。

在以往理论框架中,氮化铌的临界温度是膜厚度或室温下检测电阻的函数。研究小组进行了一系列实验,他们保持厚度或“薄膜电阻”(单位面积的材料电阻)不变而改变其他参数,然后检测临界温度的变化。结果一种清晰的关系显现出来:厚度乘以临界温度等于一个常数A除以薄膜电阻的B次幂:dTc=ARs-B,d为薄膜厚度,Tc为临界温度,Rs为薄膜电阻,A、B为常数。

推导出这一公式后,伊夫里查了过去46年相关文献中多种超导材料的数据,进行再次检验。拓宽到其他超导体后,他发现对每种新材料,公式中的常数A和B都是不同的,但方程通式对三十多种不同的超导体都适用。而且A和B之间呈直线关系,由此还能把公式中的常数简化为一个。更有趣的是,在AB关系直线的两端,材料有着完全不同的物理性质。在顶端是高度混乱无序的,在底端则更加有序。

“迄今为止还没有一个广为接受的理论,能从临界温度和薄膜电阻、厚度之间的关系上解释这么多种材料。目前有许多模型,但不能预测这么多。”法国替代能源与原子能委员会超导研究员克劳德·查普尔说,“这对技术应用来说非常便利。以往在成果出来以前,没人知道设计的超导膜能否用于设备,现在按这个法则来选,事先就已知道它是不是好用。” 科技日报

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