Understanding Room Temperature Superconductivity

室温超导体could transform everything from electrical grids to particle
accelerators to computers, but researchers are still trying to understand how these materials function on the atomic level.

Recently, NC State physicist Lex Kemper was a member of an international team that published a paper in科学on the unique properties of a material called yttrium barium copper oxide, or YBCO.

The team found that YBCO’s superconductivity is intertwined in unexpected ways with another phenomenon known as charge density waves (CDWs), or ripples in the density of electrons in the material. These CDWs get stronger when YBCO’s superconductivity is switched off. However, they were surprised to find the CDWs also suddenly became more spatially organized, suggesting superconductivity somehow fundamentally shapes the form of the CDWs at the nanoscale.

So what does this mean? The Abstract asked Kemper to share his insights.

TA:The search for room temperature superconductors could transform a lot of industries. In this paper, you looked at the connection between superconductivity and charge density waves in a material called YBCO. Let’s start with some basic definitions – what gives a material superconductivity?

Kemper:This is a really good question. We know fromBCS理论这种超导性可能发生，因为两个电子可以通过晶格振动间接相互作用，这是一种。它们形成了一个称为库珀对的绑定对，当材料中的所有相关电子都会得到一种称为超导性的状态时。现在，该理论并不直接适用于YBCO，这刺激了数十年的研究来弄清楚这些材料中发生了什么。目前，我们认为结合力是由材料中的磁波动提供的，而不是晶格振动。

TA:What is a charge density wave?

Kemper:Imagine you have a line of people, all equally spaced – that’s your starting structure. Now, have each set of two people pair up and stand slightly closer together – that’s the easiest way to see a charge density wave. In essence, it’s an additional pattern on top of the one that already existed. In YBCO, we think that this additional patterning occurs due to the electrons acting alone, rather than the atoms being involved.

TA:When you used laser pulses to “switch off” the superconductivity in the YBCO, you noticed that the charge density waves grew both stronger and more organized, meaning that superconductivity and charge density waves are somehow connected at the nanoscale. What does this mean?

Kemper:What this study showed isn’t so much a path forward to finding or creating high temperature superconductors; rather, it is a step in understanding the fundamental physics at play. We found that suppressing superconductivity causes the charge density waves to keep their pattern over much longer length scales – indicating they compete, but in a nanoscale structured way. This sheds new light on the problem of coexisting/intertwined order we see in these materials.

TA:为什么这种交织的顺序被认为是“问题”，或者我们需要进一步研究的东西？我们根本不明白为什么/如何发生？它会干扰我们利用材料某些特性的能力吗？

Kemper:简而言之，我们对为什么这种材料超导能力，为什么表现出电荷密度波，更不用说这两者的组合了！理解物理学事物的一种好方法是稍微打扰它，看看它的反应方式（这几乎是所有实验的工作方式，以及许多材料的特性如何产生）。在这种情况下，我们用超快的激光脉冲扰动，并观察到了最终的动态 - 它告诉了我们一些我们以前不知道的新事物。在这种情况下，它揭示了一种纳米级图案的存在，并排除了其他几个（是否有纳米级）模式选择。

TA:What are the next steps with this work?

Kemper:The next steps are to refine the experiment and theory, and to try to come up with new ways of looking at this problem. More broadly, we hope that the field incorporates this work in how they think about the fundamental physics of charge density waves and superconductivity in these materials.

TA:Do you think we’ll get to usable room temperature superconductors in the near future?

Kemper:This is a really good question. I hope so. What I expect is that if occurs, it will come from an unexpected corner of the vast ocean of possibilities that we haven’t explored yet.