创新背景

在超导现象中，成对的电子不受阻碍地飞行，导致材料显示为零电阻。然而，当电子通过不纯的材料时，或者当超导性被破坏时，电子就会受到阻碍。

创新过程

理论家们已经提出了许多有望显示新的电子特性的新材料，而在一个稳定的实验环境中，大量这样的材料已经成熟。第二种方法是测试和改进已知材料，特别是超薄膜，其中一些是超导体。

利用第二种方法，研究人员发现了一种超导材料，即使暴露在磁场中也能保持其超导性。根据传统理论的预测，通常情况下，磁场会破坏超导性。

破坏超导性的主要因素有三：温度升高、暴露在磁场中或携带高密度电流。此外，这些因素是相互关联的：环境越温暖，破坏其超导性所需的临界磁场就越小。然而，在新研究中，研究人员测试了一种具有不同电子特性的材料，并证明了它的超导性比理论认为的更能抵抗外部磁场。

研究人员从一个普通的硅衬底开始，在其上铺设了许多薄的材料晶体层，如碲化铋和碲化铅。顶部的灰色锡层只有几个原子层厚，此时锡层实际上变成了二维的；该层中的电子只能在锡的平面内移动，不能上下移动。早期的理论工作表明，这种多层材料将具有不同的电子特性，而其他研究人员意外地发现，这些薄膜具有超导性。他们将这种材料冷却到极低的温度以进一步研究超导性，并发现了意想不到的反常行为。

这项研究的关键是电子的一种被称为自旋的量子特性。电子的自旋是指它的角动量；这种性质可以用大小和方向来衡量。在正常的超导材料中，自旋相反的电子会形成库珀对，这种粒子负责超导。在块状材料中，自旋可以指向任何方向。然而，在某些薄膜中，自旋的方向与材料的底层电子结构耦合，导致自旋倾向于指向“平面外”。

然而，当电子暴露在磁场中时，电子的自旋倾向于与磁场的方向一致。在对锡层的研究中，研究团队在“平面内”施加了一个大磁场，意思是与纸平行。他们发现，要改变自旋方向，从而消除超导，所需的磁场强度要比现有理论预测的高出40%，而且只有当实验温度接近绝对零度时，这种效应才会显现出来。

创新关键点

这项研究的关键是电子的一种被称为自旋的量子特性。电子的自旋是指它的角动量；这种性质可以用大小和方向来衡量。

创新价值

通过这项研究所发现的新材料有望显示新的电子特性。

Innovative development of new "superconducting films" can resist the blocking force of magnets

Theorists have proposed many new materials promising to display new electronic properties, and a large number of such materials have matured in a stable experimental environment. The second approach is to test and improve known materials, particularly ultrathin films, some of which are superconductors.

Using the second method, the researchers found a superconducting material that retains its superconductivity even when exposed to a magnetic field. Conventional theory predicts that, in general, magnetic fields destroy superconductivity.

Superconductivity is broken by three main factors: increased temperature, exposure to a magnetic field, or carrying a high density of current. Moreover, these factors are interrelated: the warmer the environment, the smaller the critical magnetic field needed to disrupt its superconductivity. In the new study, however, the researchers tested a material with different electronic properties and demonstrated that its superconductivity is more resistant to external magnetic fields than theory suggests.

The researchers started with an ordinary silicon substrate and laid many thin crystalline layers of materials, such as bismuth telluride and lead telluride, on top of it. The gray tin layer at the top is only a few atomic layers thick, at which point the tin layer actually becomes two-dimensional; The electrons in this layer can only move in the plane of the tin, not up or down. Early theoretical work suggested that such multilayered materials would have different electronic properties, while other researchers unexpectedly found that these thin films were superconducting. They cooled the material to extremely low temperatures to further study superconductivity, and found unexpected abnormal behavior.

The key to this research is a quantum property of electrons called spin. The spin of an electron is its angular momentum; This property can be measured in terms of magnitude and direction. In normal superconducting materials, electrons with opposite spins form Cooper pairs, the particles responsible for superconducting. In bulk, the spin can point in any direction. In some films, however, the direction of the spin is coupled to the underlying electronic structure of the material, causing the spin to tend to point "out of plane".

However, when an electron is exposed to a magnetic field, its spin tends to align with the direction of the field. In their study of the tin layer, the team applied a large magnetic field "in-plane," meaning parallel to the paper. They found that the magnetic field needed to change the direction of the spin so as to eliminate superconductivity would be 40 percent stronger than current theory predicts, and that the effect would only be apparent when the experimental temperature was close to absolute zero.