In fact, the point of view is very simple, that is to say, everyone should understand that this thing is not just room temperature superconductivity. This phenomenon is completely new. At present, it is still controversial whether what they see is superconducting signal.

Introduce the original author of the work, Hu. It turned out that he was a doctor in Professor Wang Nanlin's group, who had just been transferred from Chinese Academy of Sciences to Quantum Center, and later graduated to Hamburg as a postdoctoral fellow.

First, superconductivity. Everyone knows that superconductivity means that when the temperature is lower than a certain value, the resistance disappears and the magnetic field is discharged from the superconductor. For conventional superconductors, such as Hg and MgB2, their superconducting transition temperature is very low (about ~30K). Of course, it can be very high under special conditions, such as the recent work of Max Planck Institute in Germany. The superconductivity of H2S can reach about 190K under the condition of adding ultra-high pressure (I forgot the connection on arxiv, but found a supplement). For copper-based superconductors discovered in 1980s and iron-based superconductors discovered in 20th century, their superconducting temperatures are much higher than those of conventional superconductors. For example, the HgBa2CuO4+delta system can have 94K. In copper-based superconductors, the structure bearing superconductivity is CuO2 surface. At first, everyone speculated that the more planes, the better superconductivity (the specific logic will not be detailed here). As a result, we went to the second and third floors and found that under pressure, we could reach 138K and 168K respectively (it may be a memory error, and the general values should be correct). But not after that. Later, a group of people thought that this thing could improve the superconducting transition temperature by making a thin film, so a group of people in Fudan made a FeSe thin film, which greatly improved the superconducting temperature compared with the iron matrix material. However, these distances are far from the normal temperature.

Then talk about ultrafast spectra in condensed matter in recent years. I really don't understand the principle and history of superluminal, so I won't mention it. Simply put, when the electromagnetic field hits the material, it will inevitably couple with the points in the crystal and the system, thus causing excitation in the system. Generally speaking, we study the near-equilibrium state, the Fermi surface behavior that determines the electrical properties of materials, and the lattice dynamic structure is stable. But what happens when a beam of light just hits the material and the system is far from equilibrium? This is the idea of using ultrafast spectroscopy in the field of condensed matter. We can observe transmission, reflection, or use it for angle-resolved photoelectron spectroscopy, and study the story of Brillouin zone of the system in various ways.

Okay, this job. 1 1 year, it is found that the crystal lattice can be "melted" if terahertz laser is used (the energy is similar to that of phonons). In some complex oxides, we can use it to melt some electronic sequences, leading to the phase transition from insulator to metal, and then induce superconductivity. Surprisingly, everyone actually observed the normal temperature signal in the YBa2Cu3O6+x system. But this signal can only last ps, and the physics they observed can be said to be time domain. The mainstream view is still unclear whether what they see is superconductivity, which is controversial in academic circles. This can be considered as "a dose of healthy skeptism". Their recent article said that they took advantage of the strong coupling between ir phonon mode and Raman phonon mode, and the symmetric name of Raman phonon mode is A 1g in 4. These four Raman phonon modes all correspond to the approach of the O atom of apical (an oxygen atom at the edge of CuO2 surface, which is common in all copper-based superconductors) to the CuO2 surface and the buckling of the CuO2 surface itself. In the buckling mode, there are various indications that it seems to be equivalent to a higher doping (in these systems, changing doping at ordinary times will change the transition temperature), and it will also suppress electron sequences such as electron density wave sequence (CDW) (which is currently considered to have an inhibitory effect on superconductivity). However, Nature, published on February 4, 65438, also pointed out that these are the beginning of the research on this thing.

Their work can only be realized in the structure of double-layer CuO2 plane, because of the symmetry of ir mode and Raman mode (not to mention in detail). Therefore, Hu is also actively looking for high-quality samples of the double-layer HgBaCuO single crystal just grown by Ethan, a teacher group of Peking University.

In my opinion, the significance of this phenomenon is more to bring a new angle to the basic research of superconductivity (in other words, this field has been heated up again, although it is the king of condensed matter, everyone has been speculating for many years). In the non-equilibrium state, we can realize many system States that cannot be realized in the equilibrium state, so that some orders are suppressed and some orders are enhanced. Compared with the past research, we can better clarify the clue of the complex problem of high temperature superconductivity (in other words, in addition to accumulating experimental data, everyone's understanding of superconductivity in the past remained in phenomenology). The general idea of high temperature superconductivity research is: anyway, it is hopeless for us to study the superconducting phase itself, so let's study the possible phase at the edge of the superconducting phase. A series of electronic sequences discovered in the past 20 years, such as stripe phase, pseudo energy gap, CDW, SDW, double magnon, etc., all appear near superconductivity, and they may interact before superconductivity. Understanding the relationship between them is indeed a breakthrough in understanding the principle of high temperature superconductivity. If everything in this system is mixed together, it is naturally difficult to study. If something can be different, it will be interesting. I hope ultrafast spectroscopy can bring such an opportunity.

Chen Jianchi's answer (7 votes):

Because Ben read a lot of papers and history about Supercon before class, I'll say some bullshit first.

Structure of yttrium, barium, copper and oxygen:

As you can see, YBCO contains CuO2 bilayer plane, CuO4 band, and CuO chain. The principle of this study is the change of energy band structure and charge transfer of CuO2 plane and CuO chain. In fact, as you can see in this article, YBCO has CuO2 double plane, CuO4 band, and CuO chain. The principle of this study is the change of energy band structure and charge transfer of CuO2 plane and CuO chain. In fact, as stated in the article "Self-doping process between planes and chains in the transition from metal to superconductor: scientific report: Nature Publishing Group", the interaction between them has always been one of the focuses of superconducting research.

The essence of this study is to guide YBCO into excited state with ultrashort pulse laser. In the transient process of induction, the distance between oxygen and copper atoms in CuO chain is shortened by 2.2-2.4 picometers (10- 12m), which leads to the reduction of its energy band by several tenths of mev. Because these energy bands are very close to their Fermi energy levels in the equilibrium state, the orbital hybridization between CuO _ 2 plane and CuO chain is greatly reduced due to this energy change, thus changing the shape and properties of its fermi surface and making it stronger.

Symmetry and high hole doping may also be the reasons for its transient superconducting characteristics at room temperature of 300K K.

Say something human.

Is this a breakthrough?

Yes At present, the research on the structural change of transient materials is still not perfect, so it is of great reference significance to observe the structure with LCLS synchronous laser in this paper. At the same time, this study makes us realize the great potential of laser-induced structural changes of materials, which opens the way for further study on the interaction between laser and alloy in the future.

Is it revolutionary?

I don't know, but I don't think so. First of all, in the sense of superconductivity, its principle is much lower than room temperature. . . The same is true for the explanation of superconducting D symmetry, which was first verified in YBCO. This study found that laser can temporarily strengthen D symmetry at room temperature, but it has not revolutionized our understanding of superconductivity. Secondly, some phenomena in this study cannot be explained quantitatively, and many qualitative words and speculative sentences are used in this paper. Further calculation and analysis are needed.

Nature original:/nature/journal/v 516/n7529/full/nature13875.html.

(Access is required to read the full text)

Liu Ao's answer (3 votes):

Room temperature superconductivity has been reported in the shell network, and the dream is no longer far away.

In short, researchers at Max Planck Institute discovered in 20 13 that YBaCuO would temporarily become a room temperature superconductor in a short time after being irradiated by infrared laser, but the specific reason is not clear. In 20 14, they used LCLS as laser source to measure the structural changes of YBaCuO crystal under infrared laser irradiation, and found that infrared laser caused tiny (pm) displacement of atoms in YBaCuO, so instantaneous room temperature superconductivity appeared. This discovery may be helpful to inspire people to find room temperature superconducting materials.

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This is the first time I have heard of LCLS, the most powerful laser cannon in the world. When I heard synchrotron radiation before, I thought NB was too good (really ignorant = = #). Only this light source can see the atomic displacement of 2pm.

But does such a strong laser source really not cause greater atomic displacement? (Or directly fry the sample into slag ...) Besides, how can 2pm displacement be distinguished from thermal vibration (sound wave)? I haven't read the article specifically, but I think these questions are answered in the paper.