Shulou(Shulou.com)11/24 Report--

[Xin Zhiyuan introduction] the room temperature superconducting reproduction experiment has entered a period of great explosion! Beihang said in two articles that LK-99 superconductivity could not be found, but researchers at the US National Laboratory confirmed that LK-99 did exist in theory through calculations.

The room temperature superconductivity of the Korean team has triggered a comeback frenzy in laboratories around the world.

Just now, there was another breaking news.

16:13 on July 31, Beihang researchers submitted a paper on arXiv, saying that the experimental results did not find the superconductivity of LK-99.

The X-ray diffraction patterns of the LK-99 samples they obtained were the same as those of the South Korean team, but huge diamagnetism and magnetic levitation were not observed.

In terms of electrical transport properties, LK-99 is more like a semiconductor; in terms of resistivity, LK-99 does not match the zero resistance of superconductors.

At about the same time (17:58 on July 31), researchers at the US National Laboratory submitted an arXiv paper that confirmed that LK-99 has the characteristics of Fermi level flat band of high temperature superconductors.

The researchers calculated the modified lead apatite by density functional theory using the calculation power of the U.S. Department of Energy, and found that there is a flat band that can cross the Fermi level, and this structure also exists in many known high temperature superconductors. Therefore, LK-99 may have superconductivity.

As soon as the two papers were published, netizens were instantly agitated!

Now, these two papers are on Hacker News's hot list Top 2.

Beihang team: no superconductivity was found just now, the Beihang team issued two papers in succession on arxiv, suspected to deny the superconductivity of LK-99, and instantly detonated Zhihu hot search.

In the first paper, the researchers said no suspension of the compound was found and needed to be reviewed.

Paper address: https://arxiv.org/pdf/2307.16802.pdf

The researchers first synthesized Pb2SO5 and Cu3P step by step.

Then the Pb10-xCux (PO4) 6O compound was sintered from these two materials.

The results show that the XRD of the experimental product is similar to the modified lead apatite XRD of the Korean team. It is found that contrary to the claimed superconductivity, Pb10-xCux (PO4) 6O compounds exhibit semiconductor-like transport behavior.

Its room temperature resistivity is as high as:

However, the x-ray diffraction spectra of the researchers' compounds are very consistent with the previously reported structural data.

In addition, at room temperature, the

Pellets are placed in commercial use.

When there is no repulsion on the magnet, no magnetic levitation is observed.

These results suggest that the superconductivity of modified lead apatite (LK-99) at room temperature needs to be re-discussed, especially in terms of electrical transport properties.

The content of the paper summarized by Claude, only for reference, is the research on the structure of LK-99 jointly done by Beihang and Shenyang National Laboratory of Materials Science of the Chinese Academy of Sciences.

The results probably show that after the introduction of copper, there is a change from insulator to metal, and the volume is reduced.

Paper address: https://arxiv.org/pdf/2307.16040.pdf

In this paper, the electronic structures of LK-99 and its parent compounds were calculated and studied by using the first principle, in order to clarify the doping effect of copper.

The results show that the parent compound

It is an insulator, and doping copper will cause the metal transformation of the insulator, resulting in volume shrinkage.

The energy band structure of LK-99 near Fermi level is characterized by a semi-filled and a completely filled flat band.

These two flat bands come from the mixing of the 2p orbitals of the O atom occupied by 1p4 and the 3D orbitals of Cu with the 2p orbitals of their nearest neighbor O atoms.

Interestingly, the researchers observed four van Hove singularities on these two flat bands, indicating the instability of electron-oriented structural distortion at low temperatures.

However, there is no final conclusion as to whether the material is superconducting or not.

All in all, the latest two studies of Beihang, on the one hand, question the superconductivity of LK-99 through reproduction experiments, but on the other hand, through calculation and simulation, it is concluded that the structure of LK-99 has a flat band of Fermi level.

The argument for LK-99 seems to be less clear, and it is difficult to judge whether it is a superconducting material or not.

Us National Laboratory: simulation found superconducting characteristics A few hours ago, researchers at Lawrence Berkeley National Laboratory submitted an arXiv paper claiming to have confirmed the existence of superconducting characteristics of LK-99.

Specifically, it is found that the isolated flat band of Fermi level is the symbol of superconducting crystal, and LK-99 also has this characteristic.

In this paper, the author simulates the situation of the material proposed by South Korea, that is, copper atoms infiltrate into the crystal structure and replace lead atoms, causing the crystal to produce slight strain and contract by 0.5%.

According to reports, this unique structure is put forward in order to realize this magical feature.

Paper address: https://arxiv.org/pdf/2307.16892.pdf

Sinn é ad Griffin, a researcher at Lawrence Berkeley National Laboratory, simulated this phenomenon using the math of the U.S. Department of Energy.

The authors used a calculation method called density functional theory to explore the properties of copper-substituted apatite.

The researchers found that LK-99 has some special energy band structures near the Fermi level, an important energy level, which are called "isolated flat bands".

These isolated flat bands are signs of high transition temperatures in some known families of superconductors.

There are two origins of isolated flat bands in LK-99.

One of the sources is that copper ions cause structural distortion, that is, changes in the arrangement of atoms. Another source is that a special charge density wave is formed by the isolated electron pair of lead ion.

The authors point out that these results suggest that a simplified model, the "double-band model", can better describe the low-energy physical behavior in this material.

At the same time, the author also studied what changes will happen to the "electronic structure" of this material, that is, what conduction pathways are available in the material.

It is found that the conduction path of electrons happens to be in the appropriate condition and position to make them "superconducting".

More specifically, they are close to "Fermi noodles", which are like the sea level of electricity, such as "0 feet above sea level".

It is believed that the more conduction paths near the Fermi surface, the higher the superconducting temperature. For example, because of the "ground effect", aircraft are more likely to fly closer to the ocean surface, thus gaining more lift.

In this paper, this picture shows the "bands" or electronic pathways that intersect up and down Fermi's surface.

These interesting conduction paths are formed only when copper atoms infiltrate into less likely positions or "higher energy" binding sites in the lattice.

This means that the material is difficult to synthesize because only a small portion of the copper in the crystal is in the right place.

The content of the paper summarized by Claude is only for reference to the Korean paper to make a revision around 9: 00 this morning, and the revised paper on room temperature superconductivity has also been released! Netizens ran to tell each other excitedly.

Now, when you log on to arXiv, you can see that the six authors' papers on room temperature superconductivity have been revised and submitted for the second edition on the 29th.

What is the difference between the second version and the first version? After comparison, it is found that, in fact, these are the only two important changes.

In the first place, a key chart has been modified to two.

It seems that the y-axis magnetic susceptibility error mentioned by the author Hyun-Tak Kim earlier should have been modified in the figure on the right.

Left: the old version; right: the second part of the new version is that the Korean tag has been deleted.

But some netizens questioned, "the error of Latex still exists. It occurred twice before, but now it has been reduced to one." Is it so difficult to proofread before submitting it? "

In short, the substantive change is just a picture, which can not help but let the majority of netizens feel disappointed.

Prior to this, three works of the six-person paper, Hyun-Tak Kim, told the Daily Business News that there were indeed some minor errors in the paper, which the team was already correcting and would upload a new version as soon as possible.

On July 28, Hyun-Tak Kim said in an email that there were two data errors in the y-axis susceptibility, which he would immediately correct in another email. Hyun-Tak Kim said that he had uploaded the revised version on the 27th, which is expected to be displayed on arXiv on Tuesday.

Another "room temperature superconductor" is coming? Interestingly, Taj Quantum, a blockchain company, claims to have also achieved room temperature superconductivity and has applied for a patent.

Just this morning, they released photos of superconductors and introduced them as a kind of graphene foam.

The original patent text can be downloaded from the United States Patent Office.

Https://kdocs.cn/l/caKwDx25VrCU?f=201

However, even if this thing is true, it is not the first type of superconductivity we are talking about.

And the vast majority of netizens are skeptical about this, thinking that the company is more hot.

Live netizens, Andrew McCalip, who launched the live LK-99 reproduction process before asking the original work for help online, are still waiting for the firing of the material in the second step.

He said he had a problem with his first synthetic CuP, but the Polish-made CuP he ordered would arrive on Wednesday morning. This means that the first final reaction will begin on Wednesday, and the first LK-99 sample is likely to appear on Thursday.

However, during the progress of the Andrew live broadcast experiment, he mentioned that he was worried about the lack of details in the paper, and it was difficult to grasp the process of making LK-99 in the experiment.

Enthusiastic netizens provided Andrew with a website to ask Lee questions about the preparation of LK-99:

Website address: https://qcentre.co.kr/qna

In this case, Andrew's doubts in the course of the experiment can be regarded as a leak.

For example, dealing with the details of the experiment:

Does the precursor material have to reach the purity level? What is the required particle size?

Do you need to take any necessary pretreatment steps before using it?

Is the environment of Lanarkite reaction air or vacuum?

How sensitive is LK99 to the duration of the final 925 °C step?

There are also questions about the results of the experiment:

Can you elaborate on the differences between the observed bulk materials and thin films?

Is the composition of bulk material the same as that of thin film?

What is the repeatability of the prescribed formula, and is the SC behavior random in the sample?

In patent figure 22, which region does the resistivity value come from? Light gray or dark gray area?

Wait a minute.

Now, Andrew has submitted his question to the website.

It is conceivable that more experimental results will be reproduced in the next few days.

The achievements of researchers around the world will be put together to verify whether human beings can take off the holy grail of room temperature superconductivity and enter a new era.

Reference:

Https://twitter.com/andrewmccalip/status/1685871360948748288

Https://www.zhihu.com/question/614426480/answer/3142610238

Https://arxiv.org/pdf/2307.16802.pdf

Https://arxiv.org/pdf/2307.16040.pdf

Https://arxiv.org/pdf/2307.16892.pdf

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