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新发现的超导电流只沿材料的边缘流动

  lectricity flows without resistance on the rim of molybdenum ditelluride

  电流在二碲化钼的边缘无阻力流动

  The material molybdenum ditelluride can host a superconducting current that is constrained to travel around its edge,physicists report.

  物理学家报告,二碲化钼材料可以承载超导电流,该电流被限制在其边缘流动。

  Superconductors are getting edgy.

  超导体变得前卫。

  For the first time,scientists have spotted a superconducting current traveling along the edge of a material,like a trail of ants crawling along the rim of a dinner plate without venturing into its middle.

  科学家们第一次发现了一种超导电流,它沿着材料的边缘行进,就像一团蚂蚁沿着餐盘的边缘爬行而没有进入其中间。

  Normally,such superconducting currents,in which electricity flows without any loss of energy,permeate an entire material.But in a thin sheet of molybdenum ditelluride chilled to near absolute zero,the interior and edge make up two distinct superconductors,physicist Nai Phuan Ong and colleagues report in the May 1 Science.The two superconductors are“basically ignoring each other,”says Ong,of Princeton University.

  通常,电流流过而没有任何能量损失的这种超导电流会渗透到整个材料中。但是物理学家奈Phuan Ong和他的同事在5月1日的《Science》杂志上报告说,在冷却至绝对零附近的二碲化钼薄板中,内部和边缘构成了两个截然不同的超导体。普林斯顿大学的Ong说,这两种超导体“基本上互相忽略”。

  This distinction between exterior and interior makes molybdenum ditelluride an example of what are called topological materials.Their behavior is closely tied to the mathematical field of topology,in which shapes are considered distinct only if one can’t be molded into another without cutting or melding(SN:10/4/16).In topological insulators,electric currents can flow on the surface of a material but not the interior,like a potato covered in tinfoil(SN:5/7/10).

  外部和内部之间的这种区别使二碲化钼成为所谓的拓扑材料的一个例子。它们的行为与拓扑学的数学领域紧密相关,在拓扑学中,只有在不进行切割或融合就无法成型为另一种形状的情况下,才认为形状是不同的(SN:10/4/16)。在拓扑绝缘体中,电流可以在材料的表面上流动,但不能在内部流动,就像覆有锡箔的马铃薯一样(SN:5/7/10)。

  拓扑超导体在其内部也具有超导体

  Likewise,topological superconductors are superconducting in their interiors and behave differently on their surfaces.Although some researchers suspected topological superconductors might also host superconducting current on their edges,none had yet been found.But the new observation is“extremely convincing,”says physical chemist Claudia Felser of the Max Planck Institute for Chemical Physics of Solids in Dresden,Germany,who was not involved with the research.“It’s really,really super exciting.”

  同样,拓扑超导体在其内部也具有超导体,并且在其表面上具有不同的行为。尽管一些研究人员怀疑拓扑超导体也可能在其边缘承载超导电流,但尚未发现。但是德国德累斯顿的马克斯·普朗克固体化学物理研究所的物理化学家Claudia Felser说,但是这一新发现“极具说服力”。“真的,真的非常令人兴奋。”

  Molybdenum ditelluride is a metal-like compound called a Weyl semimetal(SN:7/16/15).Its unusual properties might mean it could harbor Majorana fermions,disturbances within a material that scientists hope to use to create better quantum computers.Such topological quantum computers are expected to resist the jitter that impairs quantum calculations(SN:7/20/17).

  二碲化钼是一种类似Weyl半金属(SN:7/16/15)。它不寻常的特性可能意味着它可能藏有马里亚纳费米子,这是科学家希望用来制造更好的量子计算机的材料中的干扰。此类拓扑量子计算机有望抵抗损害量子计算的抖动(SN:7/20/17)。

  In their experiment,Ong and colleagues gradually ramped up the magnetic field on the material.They simultaneously measured how much they could increase the electric current before the superconducting state was lost,a value known as the critical current.As the magnetic field increased,the critical current oscillated,getting larger,smaller,and larger again in a repeating pattern—a hallmark of an edge superconductor.

  在实验中,Ong及其同事逐渐提高了材料上的磁场。他们同时测量了在失去超导状态之前可以增加多少电流,该值称为临界电流。随着磁场的增加,临界电流振荡,以重复的模式变大,变小,然后又变大,这是边缘超导体的标志。

  The oscillation results from the weird physics of superconductors,in which electrons form partnerships called Cooper pairs.The pairs act as a unified whole,all taking on the same quantum state,or wave function,which determines the probability of a particle being found at a particular location.

  这种振荡是由超导体奇怪的物理现象引起的,在这种现象中,电子会形成一种叫做“库珀对”的运动形式。这些粒子对作为一个统一的整体,都具有相同的量子态或波函数,这决定了在特定位置发现粒子的可能性。

  A superconducting current(white arrows)runs around the edge of a thin sheet of molybdenum ditelluride(illustrated on right)in a magnetic field(black arrows).A similar effect in a ring of superconductor(left)was seen in a classic study known as the Little-Parks experiment.

  超导电流(白色箭头)在磁场中绕着一层二碲化钼薄膜(如右图所示)的边缘流动(黑色箭头)。在一项称为Little-Parks实验的经典研究中,在超导体环(左)中也有类似的效果。

  波函数的一种叫做相位的性质类似于悬挂在房间边缘的派对彩带的扭曲

  A property of the wave function called the phase is analogous to twists in a party streamer hung around the edges of a room,Ong says.If connected at the ends,the party streamer can twist once or twice,but never 1.2 times,for example,because the ends wouldn’t align.Similarly,the phase must make a full number of twists around the material.The interplay between the increasing magnetic field and the twisting constraint causes the critical current to oscillate.

  Ong说,波函数的一种叫做相位的性质类似于悬挂在房间边缘的派对彩带的扭曲。如果连接在两端,则派对彩带可以扭曲一到两次,但不能扭曲1.2倍,因为两端无法对齐。同样,这个阶段必须在材料周围做大量的扭曲。不断增加的磁场与扭曲约束之间的相互作用导致临界电流振荡。

  A classic 1960s study known as the Little-Parks experiment is closely tied to the new work.In that study,a superconductor shaped like a cylinder exhibited related oscillations in a changing magnetic field.But in Ong and colleagues’version,the superconducting current runs around the edge of a solid chunk of material rather than a physical cylinder.

  1960年代的经典研究称为Little-Parks实验,它与这项新研究密切相关。在这项研究中,形状像圆柱体的超导体在不断变化的磁场中表现出相关的振荡。但在Ong及其同事的版本中,超导电流围绕的是固体材料而不是物理圆柱体的边缘。

  “It’s a very clever and beautiful way of assessing whether or not there’s an edge current”that is superconducting,says physicist Smitha Vishveshwara of the University of Illinois at Urbana-Champaign,who was not involved with the research.

  伊利诺伊大学厄巴纳-香槟分校的物理学家Smitha Vishveshwara说:“这是一种评估是否存在边缘电流的非常聪明而优美的方法。”,他没有参与这项研究。
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