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物理学家发现了一系列坚固的超导石墨烯结构

Physicists discover a “family” of robust, superconducting graphene structures

When it comes to graphene, it appears that superconductivity runs in the family.

说到石墨烯,似乎首先出现的名词是超导性。

Graphene is a single-atom-thin material that can be exfoliated from the same graphite that is found in pencil lead. The ultrathin material is made entirely from carbon atoms that are arranged in a simple hexagonal pattern, similar to that of chicken wire. Since its isolation in 2004, graphene has been found to embody numerous remarkable properties in its single-layer form.

石墨烯是一种单原子薄材料,可以从铅笔芯中发现的相同石墨中剥离。这种超薄材料完全由碳原子制成,碳原子以简单的六边形排列,类似于铁丝网。自2004年分离以来,人们发现石墨烯以单层形式表现出许多显著的特性。

In 2018, MIT researchers found that if two graphene layers are stacked at a very specific “magic” angle, the twisted bilayer structure could exhibit robust superconductivity, a widely sought material state in which an electrical current can flow through with zero energy loss. Recently, the same group found a similar superconductive state exists in twisted trilayer graphene — a structure made from three graphene layers stacked at a precise, new magic angle.

2018年,麻省理工学院的研究人员发现,如果两个石墨烯层以非常特定的“魔法”角度堆叠,扭曲的双层结构可能会表现出强大的超导性,这是一种广泛寻求的材料状态,在这种状态下,电流可以以零能量损失流过。最近,同一个研究小组发现,扭曲的三层石墨烯中存在类似的超导状态,这是一种由三层石墨烯以精确、新的魔法角度堆叠而成的结构。

Now the team reports that — you guessed it — four and five graphene layers can be twisted and stacked at new magic angles to elicit robust superconductivity at low temperatures. This latest discovery, published this week in Nature Materials,  establishes the various twisted and stacked configurations of graphene as the first known “family” of multilayer magic-angle superconductors. The team also identified similarities and differences between graphene family members.

现在,该团队报告说——你猜对了——四层和五层石墨烯可以扭曲并以新的魔角堆叠,从而在低温下产生强大的超导性。这项最新发现发表在本周的《自然材料》杂志上,确立了石墨烯的各种扭曲和堆叠结构,成为第一个已知的多层魔角超导体“家族”。该团队还确定了石墨烯家族成员之间的异同。

The findings could serve as a blueprint for designing practical, room-temperature superconductors. If the properties among family members could be replicated in other, naturally conductive materials, they could be harnessed, for instance, to deliver electricity without dissipation or build magnetically levitating trains that run without friction.

这些发现可以作为设计实用室温超导体的蓝图。如果家庭成员之间的特性可以在其他自然导电材料中复制,那么可以利用它们,例如,在不耗散的情况下输送电力,或者建造运行时没有摩擦的磁悬浮列车。

“The magic-angle graphene system is now a legitimate ‘family,’ beyond a couple of systems,” says lead author Jeong Min (Jane) Park, a graduate student in MIT’s Department of Physics. “Having this family is particularly meaningful because it provides a way to design robust superconductors.”

“魔角石墨烯系统现在是一个合法的’家族’,超越了几个系统,”首席作者郑敏(简)帕克说,她是麻省理工学院物理系的研究生。“拥有这个家族特别有意义,因为它提供了一种设计坚固超导体的方法。”

Park’s MIT co-authors include Yuan Cao, Li-Qiao Xia, Shuwen Sun, and Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics, along with Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Tsukuba, Japan.

帕克与麻省理工学院的合著者包括曹元元、李巧霞、孙淑文、塞西尔和艾达·格林,物理学教授巴勃罗·贾里洛·埃雷罗,以及日本筑波国立材料科学研究所的渡边健二和谷口隆志。

“No limit”

“没有限制”

Jarillo-Herrero’s group was the first to discover magic-angle graphene, in the form of a bilayer structure of two graphene sheets placed one atop the other and slightly offset at a precise angle of 1.1 degrees. This twisted configuration, known as a moiré superlattice, transformed the material into a strong and persistent superconductor at ultralow temperatures.

贾里洛·赫雷罗的团队是第一个发现魔角石墨烯的团队,这种石墨烯是由两个石墨烯片构成的双层结构,一个置于另一个之上,以1.1度的精确角度略微偏移。这种扭曲的结构被称为莫尔超晶格,在超低温下将这种材料转变为一种强大而持久的超导体。

The researchers also found that the material exhibited a type of electronic structure known as a “flat band,” in which the material’s electrons have the same energy, regardless of their momentum. In this flat band state, and at ultracold temperatures, the normally frenetic electrons collectively slow down enough to pair up in what are known as Cooper pairs — essential ingredients of superconductivity that can flow through the material without resistance.

研究人员还发现,这种材料表现出一种称为“平带”的电子结构,在这种结构中,材料的电子具有相同的能量,而不管其动量如何。在这种平带状态下,在超低温下,通常疯狂的电子集体减速,足以形成所谓的库珀对,库珀对是超导电性的基本成分,可以在没有电阻的情况下流过材料。

While the researchers observed that twisted bilayer graphene exhibited both superconductivity and a flat band structure, it wasn’t clear whether the former arose from the latter.

虽然研究人员观察到扭曲双层石墨烯既具有超导性又具有平带结构,但尚不清楚前者是否起源于后者。

“There was no proof a flat band structure led to superconductivity,” Park says. “Other groups since then have produced other twisted structures from other materials that have some flattish band, but they didn’t really have robust superconductivity. So we wondered: Could we produce another flat band superconducting device?”

帕克说:“没有证据表明平带结构导致了超导性。”。“从那时起,其他研究小组已经用其他具有一些扁平带的材料制造了其他扭曲结构,但它们并没有真正具有强大的超导性。因此我们想知道:我们能制造出另一个扁平带超导设备吗?”

As they considered this question, a group from Harvard University derived calculations that confirmed mathematically that three graphene layers, twisted at 1.6 degrees, would exhibit also flat bands, and suggested they may superconduct. They went on to show there should be no limit to the number of graphene layers that exhibit superconductivity, if stacked and twisted in just the right way, at angles they also predicted. Finally, they proved they could mathematically relate every multilayer structure to a common flat band structure — strong proof that a flat band may lead to robust superconductivity.

当他们考虑这个问题时,来自哈佛大学的一组推导出的计算从数学上证实了三个石墨烯层在1.6度扭曲时也会表现出平带,并表明它们可能是超导体。他们继续表明,如果以正确的方式堆叠和扭曲,在他们预测的角度,表现出超导性的石墨烯层的数量应该没有限制。最后,他们证明了他们可以从数学上将每一种多层结构与一种常见的平带结构联系起来,这有力地证明了平带可能产生强大的超导电性。

Read more at News.MIT.edu

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