Physicists Make Electrons Flow Like Water

Water molecules flow together; electrons usually do not.

水分子聚集在一起；电子通常不会。

If you were asked to picture how electrons move, you could be forgiven for imagining a stream of particles sluicing down a wire like water rushing through a pipe.

如果你被要求想象电子如何运动，你可能会想象粒子流沿着电线冲下，就像水冲过管道一样。

After all, we often describe electrons as “flowing” in an “electric current.”

毕竟，我们经常将电子描述为在“电流”中“流动”。

In reality, water and electricity flow in completely different ways.

事实上，水和电以完全不同的方式流动。

Whereas water molecules move together to form a swirly, coherent substance, electrons tend to fly past one another.

水分子一起运动形成一种漩涡状、连贯的物质，而电子则倾向于相互飞过。

“Water is seeing nothing but other water,” said Cory Dean , a physicist at Columbia University, “but in an electronic system, in a wire, that’s manifestly not the case.” Water molecules unite to flow, but each electron acts on its own.

哥伦比亚大学物理学家科里·迪恩说：“水只能看到其他水，但在电子系统中，在电线中，情况显然并非如此。”水分子结合起来流动，但每个电子都单独起作用。

This every-particle-for-itself movement serves as the foundation for all of electronic theory.

这种每个粒子自为运动是所有电子理论的基础。

It explains why a warm wire resists more than a cold wire, and why a round wire conducts as well as a square wire.

它解释了为什么热线比冷线电阻更大，以及为什么圆线和方线一样导电。

But since the 1960s, theorists have suspected that electrons can be coaxed to act more like their watery counterparts, and to form an electron fluid.

但自 20 世纪 60 年代以来，理论学家怀疑电子可以被诱导使其表现得更像水状电子，并形成电子流体。

In recent years, a string of experiments has confirmed that prediction.

近年来，一系列实验证实了这一预测。

Last fall, in the most dramatic demonstration yet , Dean and his collaborators arranged for electrons to form a type of shock wave that occurs when a quickly flowing fluid crashes into a slowly flowing fluid.

去年秋天，在迄今为止最引人注目的演示中，迪恩和他的合作者安排电子形成一种冲击波，当快速流动的流体撞击缓慢流动的流体时就会发生这种冲击波。

It was a surefire sign that electrons were flowing at extremely high speeds.

这是电子以极高速度流动的明确迹象。

“That’s really the frontier right now,” said Thomas Scaffidi , a physicist at the University of California, Irvine who was not involved in the experiment.

“这确实是目前的前沿，”未参与该实验的加州大学欧文分校物理学家托马斯·斯卡菲迪 (Thomas Scaffidi) 说。

Making electrons behave like water might someday lead to the development of new kinds of electronic devices.

让电子表现得像水一样，有朝一日可能会导致新型电子设备的开发。

And extending the familiar theory of water to electrons could spawn a new way of thinking about quantum materials.

将人们熟悉的水理论扩展到电子可能会催生一种关于量子材料的新思维方式。

Andrew Lucas , a theoretical physicist at the University of Colorado, Boulder, compares electrons traveling down a wire to pinballs traveling around a pinball machine.

科罗拉多大学博尔德分校的理论物理学家安德鲁·卢卡斯将沿电线传播的电子与绕弹球机传播的弹球进行了比较。

Once they enter the playing field, pinballs bounce around in every direction, flying off flippers and bumpers.

一旦进入比赛场地，弹球就会向各个方向弹跳，从脚蹼和保险杠上飞走。

They travel up the machine, down the machine, and all around it.

它们在机器上、机器下以及机器周围移动。

Similarly, when electrons in a copper wire collide with vibrating copper atoms or with “impurities” in the metal — spots where some other atom has usurped an atom of copper — they ricochet in all directions.

同样，当铜线上的电子与振动的铜原子或金属中的“杂质”（其他原子取代了铜原子的位置）碰撞时，它们会向各个方向弹跳。

On average, pinballs do tend to travel farther down than up; in this sense they “flow” downward.

平均而言，弹球确实倾向于向下移动得比向上移动得更远。从这个意义上说，它们是向下“流动”的。

Analogously, the “flow” of electrons emerges only in an average sense; an electric field, perhaps generated by a battery, establishes an ever-so-slightly preferred direction in the wire.

类似地，电子的“流动”仅在平均意义上出现；电场（可能是由电池产生的）在电线中建立了一个稍微优选的方向。

Cory Dean, a physicist at Columbia University, leads the lab that created the most dramatic recent demonstration of an electron fluid.

哥伦比亚大学物理学家科里·迪恩 (Cory Dean) 领导的实验室创造了最近最引人注目的电子流体演示。

But this is a peculiar type of flow.

但这是一种特殊的流动类型。

An electron collides with an impurity much in the same way a hacky sack collides with the floor: It thuds more than it bounces.

电子与杂质的碰撞就像麻袋与地板的碰撞一样：撞击的声音大于弹跳的声音。

The impurity saps the electron’s energy, preventing it from building up much momentum.

杂质会消耗电子的能量，阻止其积累足够的动量。

Consequently, electrons move through a wire a bit like water seeping through packed sand, a motion physicists describe as a “dispersive” flow.

因此，电子在电线中移动，有点像水渗入填充的沙子，运动物理学家将这种运动描述为“色散”流。

In contrast, water molecules flowing down a pipe collide almost exclusively off each other.

相比之下，沿着管道流动的水分子几乎完全相互碰撞。

And when they collide, they bounce like billiard balls: They share their momentum and keep on moving.

当它们碰撞时，它们会像台球一样弹起：它们分享动力并继续移动。

This ability of water molecules to “conserve” their momentum defines the nature of liquidity.

水分子“保存”动量的能力定义了流动性的本质。

Since collisions with obstacles don’t drain their momentum, water molecules can engage in complicated collective motions, flowing in faster- and slower-moving zones and in swirling eddies.

由于与障碍物的碰撞不会耗尽它们的动量，因此水分子可以进行复杂的集体运动，在运动较快和较慢的区域以及漩涡中流动。

In 1963 Radii Gurzhi, a Soviet physicist, was the first to calculate exactly what would happen if electrons found themselves in a situation where they could only knock into each other, conserving momentum like water molecules.

1963 年，苏联物理学家拉迪·古尔吉 (Radii Gurzhi) 首次准确计算出如果电子发现自己处于只能相互碰撞、像水分子一样守恒动量的情况下会发生什么。

Gurzhi found that the difference would lie in how the electric current reacted to heat.

古尔兹发现差异在于电流对热量的反应方式。

Warming a copper wire typically impedes electric current, since vibrations in the copper atoms intensify and more greatly impede electrons.

加热铜线通常会阻碍电流，因为铜原子的振动会加剧，并且会更大程度地阻碍电子。

But Gurzhi calculated that if momentum were conserved, heat would make electrons move more readily — similar to the way warm honey is runnier than cool honey.

但古尔吉计算出，如果动量守恒，热量会使电子更容易移动——类似于热蜂蜜比冷蜂蜜更容易流动。

His observation became known as the Gurzhi effect, but it didn’t attract much attention at the time.

他的观察被称为“古尔吉效应”，但当时并没有引起太多关注。

It seemed like a theoretical curiosity, with little relevance to real electrons, trapped as they were in real-world wires “full of dirt and impurities,” Lucas said.

卢卡斯说，这似乎是一种理论上的好奇心，与真实的电子几乎没有关系，因为它们被困在现实世界的电线中，“充满污垢和杂质”。

Fifty years later, that would change.

五十年后，情况将会改变。

In 2004, Andre Geim and Konstantin Novoselov announced the discovery of graphene, a honeycomb sheet of carbon atoms they could peel off a block of pencil lead using only Scotch tape.

2004 年，安德烈·海姆 (Andre Geim) 和康斯坦丁·诺沃肖洛夫 (Konstantin Novoselov) 宣布发现了石墨烯，这是一种由碳原子组成的蜂窝状薄片，他们只需使用透明胶带即可将铅笔芯剥离下来。

The effort earned them a Nobel Prize.

这项努力为他们赢得了诺贝尔奖。

A layer of graphene was like a pinball machine with no bumpers; almost every atom was in its place.

一层石墨烯就像一台没有保险杠的弹球机；几乎每个原子都在它的位置上。

“It’s just a thermodynamically beautiful crystal.

“这只是一种热力学上美丽的晶体。

It comes out of the earth well formed, with very few impurities,” said Dean, who specializes in graphene experiments.

它从地球上出来时结构良好，杂质很少，”专门从事石墨烯实验的迪恩说。

A metallic tip just nanometers across picked up tiny variations in the graphene’s electric field, revealing a fluid shock wave where supersonic electrons suddenly slowed down.

直径只有几纳米的金属尖端拾取了石墨烯电场的微小变化，揭示了超音速电子突然减速的流体冲击波。

It took physicists about a decade to figure out how to study graphene without interference from other materials.

物理学家花了大约十年的时间才弄清楚如何在不受其他材料干扰的情况下研究石墨烯。

But when they did, they detected electrons truly flowing.

但当他们这样做时，他们检测到电子真正流动。

In one early experiment, in 2017, Geim and his collaborators carved a choke point into a strip of graphene, poured electrons through, and measured the resistance.

在 2017 年的一项早期实验中，海姆和他的合作者在一条石墨烯上刻了一个阻塞点，将电子注入其中，并测量了电阻。

They found that as they turned up the temperature, the resistance fell — the Gurzhi effect in action.

他们发现，当温度升高时，电阻会下降——古尔吉效应正在发挥作用。

And in 2022, physicists at the Weizmann Institute of Science in Israel managed to directly watch electrons flowing.

2022 年，以色列魏茨曼科学研究所的物理学家成功地直接观察到了电子的流动。

They shaped a material with some similarities to graphene, called tungsten diselenide, into a vertical wire flanked halfway down by two circles resembling Mickey Mouse ears.

他们将一种与石墨烯有些相似的材料（称为二硒化钨）塑造成一根垂直的金属丝，中间有两个类似米老鼠耳朵的圆圈。

As electrons flowed into the ears on their way down the wire, the group monitored their motion by measuring the magnetic field the electrons generated when moving around the wire.

当电子沿着电线流入耳朵时，研究小组通过测量电子绕电线移动时产生的磁场来监测它们的运动。

In doing so, they saw fluidic electric currents swirling backward into the ears — electron whirlpools.

在此过程中，他们看到流体电流向后旋转进入耳朵——电子漩涡。

The whirlpools resembled the eddies that form when part of a river’s current runs into a bend and turns upstream.

漩涡类似于河水的一部分流入拐弯处并转向上游时形成的漩涡。

“They can really see these vortices,” said Scaffidi, who collaborated with Geim’s group on another electron fluid experiment , also in 2022.

“他们真的可以看到这些漩涡，”斯卡菲迪说，他也在 2022 年与海姆的团队合作进行了另一项电子流体实验。

In 2025, Johannes Geurs, a postdoc in Dean’s lab, decided to push the idea of electron fluids “to the extreme,” Dean said.

Dean 说，2025 年，Dean 实验室的博士后 Johannes Geurs 决定将电子流体的想法推向“极致”。

Slowly moving fluids act differently from quickly moving fluids.

缓慢移动的流体的行为与快速移动的流体不同。

We can see this in the air, which is as much a fluid as water, because air molecules conserve momentum when they collide.

我们可以在空气中看到这一点，空气和水一样是流体，因为空气分子碰撞时会保持动量。

When a plane accelerates past the sound barrier in the air, it generates a shock wave known as a sonic boom.

当飞机加速穿过空气中的音障时，它会产生称为音爆的冲击波。

Geurs wondered if it was possible to break an analogous sound barrier with electrons themselves, which would lead to another sort of supersonic shock wave.

格尔斯想知道是否有可能用电子本身打破类似的音障，这将导致另一种超音速冲击波。

Johannes Geurs proposed the idea to attempt to create an electron fluid shock wave.

Johannes Geurs 提出了尝试产生电子流体冲击波的想法。

To produce the speediest electron fluid possible, he carved a strip made from two sheets of graphene into a sleek shape known as a de Laval nozzle — a shape that rocket engines use to accelerate their exhaust.

为了产生尽可能最快的电子流体，他将两片石墨烯制成的条带雕刻成光滑的形状，称为拉瓦尔喷嘴——火箭发动机用来加速排气的形状。

Then he sent electrons through the constriction formed by the nozzle, which boosted their speed beyond the rate at which ripples travel through the electron fluid.

然后，他将电子发送通过喷嘴形成的收缩，这使得电子的速度超过了波纹穿过电子流体的速度。

That’s the “speed of sound” for an electron fluid, a few hundred kilometers per second.

这就是电子流体的“声速”，每秒几百公里。

When the accelerated electrons crashed into other electrons lingering in an open region downstream of the nozzle, the slower, subsonic electrons couldn’t get out of the way fast enough, and the liquid compressed.

当加速的电子撞击喷嘴下游开放区域中的其他电子时，速度较慢的亚音速电子无法足够快地避开，液体就会被压缩。

The researchers swept a metallic tip back and forth over the sample, measuring minute changes in the electric field, and detected the pileup.

研究人员用金属尖端在样品上来回扫动，测量电场的微小变化，并检测到堆积现象。

The shock wave indicated that they had in fact broken the electron fluid’s sound barrier.

冲击波表明，他们实际上已经突破了电子液的音障。

Experiments like these allow researchers to flex and extend their control over electrons.

此类实验使研究人员能够灵活和扩展对电子的控制。

This new level of mastery could lead to novel electronics components.

这种新的掌握水平可能会带来新颖的电子元件。

For example, when electrons move like fluids, they start to respond to the shape of the channel through which they’re moving, whether it’s Mickey Mouse ears or a nozzle.

例如，当电子像流体一样移动时，它们开始对其移动通道的形状做出反应，无论是米老鼠耳朵还是喷嘴。

“By using different shapes for your device, you can realize very different physics,” Scaffidi said.

“通过为你的设备使用不同的形状，你可以实现非常不同的物理效果，”斯卡菲迪说。

These experiments could also help theorists develop an entirely new way of talking and thinking about electrons and subatomic systems.

这些实验还可以帮助理论家开发一种全新的方式来谈论和思考电子和亚原子系统。

It’s “a baby step” toward using what we know about the movement of liquids to understand quantum systems, Scaffidi said.

斯卡菲迪说，这是利用我们对液体运动的了解来理解量子系统的“一小步”。

When electrons flow like fluids, they form coherent patterns.

当电子像流体一样流动时，它们会形成连贯的图案。

Once you know some high-level properties of the fluid, such as density and viscosity, you can use standard equations to find out what the fluid will do, without needing to keep track of the motion of every last electron.

一旦您了解了流体的一些高级特性（例如密度和粘度），您就可以使用标准方程来找出流体的作用，而无需跟踪每个电子的运动。

The hope is that in other complicated quantum or semi-quantum systems, theorists might, for instance, be able to identify conservation laws that will help them recognize similar large-scale flow behavior, as one group was able to do for certain chaotic quantum circuits in 2024.

例如，我们希望在其他复杂的量子或半量子系统中，理论学家可能能够识别守恒定律，帮助他们识别类似的大规模流动行为，就像一个小组在 2024 年对某些混沌量子电路所做的那样。

Perhaps by continuing to cook up electron fluids in the lab, and by using hydrodynamics to describe the way they swirl, theorists will find a way to describe other, more enigmatic situations where electrons seem to melt away , said Lucas, who helped with some of the theory calculations for the Columbia experiment.

帮助哥伦比亚实验进行一些理论计算的卢卡斯说，也许通过在实验室中继续制备电子流体，并通过使用流体动力学来描述它们的旋转方式，理论学家将找到一种方法来描述电子似乎融化的其他更神秘的情况。

“It’s a very appealing showcase of something that can’t be explained in any textbook paradigm,” he said.

“这是一个非常吸引人的展示，展示了任何教科书范式都无法解释的东西，”他说。

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