From Almighty Scholar to Chief Scientist

Chapter 321 Landau Fermi Liquid Theory
The critical current density is an important parameter for judging the quality of superconducting materials.

Superconductors have three critical conditions, which are critical temperature, critical current density, and critical magnetic field strength. Only within these three critical conditions can they maintain a superconducting state.

Among them, the critical current density can be said to be the most important data, because it determines the current it can carry.

For example, the critical current density of the most commonly used niobium-titanium alloy is as high as 10^9A/m, at least twice that of YBCO, coupled with its good plasticity and low cost, it is often used in practical applications , even if yttrium barium copper oxide only needs liquid nitrogen to cool it, but because these cost gaps make up for the cost of liquid nitrogen and liquid helium, yttrium barium copper oxide cannot replace the status of niobium titanium alloy.

However, Lin Xiao's experiment now shows that the critical current of this new type of niobium-titanium alloy has increased by a factor of ten compared with the previous old niobium-titanium alloy.

This kind of performance is absolutely incredible. Who would have thought that the same chemical formula, the same molar mass, and the same density can be said to be the same material, but in the process of entering the superconducting state, such a situation happened!

Chen Xun was very surprised and asked: "Director Lin, why is this? Is it possible that the structure after the equivalent topological transformation according to the theory of electron topological bonding is not completely equivalent? Or is it that it can specifically enhance the strength of this material?" Critical current density?"

Lin Xiao shook his head: "This is not necessarily the case. One thing that can be revealed in the electron topological bonding theory is that for a compound, there can be many different equivalent topological forms."

"So, for different structures, the current density may increase or decrease."

"After all, superconductivity is the free movement of electrons without resistance inside the material, and the internal structure has a great influence on whether electrons can move freely."

Listening to Lin Xiao's explanation, Chen Xun nodded, but soon had another doubt: "Then how do you know that your YBCO structure has less resistance to the free movement of electrons? The theory of electron topological bonding, Shouldn't it work out?"

If this can be calculated, everyone who studies superconductivity will have to call Lin Xiao "Dad".

Because once it can be counted, Lin Xiao will provide a huge treasure for the world's superconducting community.

By then, at least hundreds of papers will be issued.

But obviously, after Chen Xun has been studying it for so long, he doesn't think that the theory of electron topological bonding can calculate this kind of thing.

Upon hearing Chen Xun's question, Lin Xiao was silent for a moment, and then said, "Feeling."

"Feeling?" Chen Xun was taken aback.

"Well, I feel that this equivalent topological structure will have very little resistance to electrons."

Chen Xun: "... Can you feel this too?"

As a professor of physics at Peking University, I don't read much, so don't lie to me.

The critical current density of a superconductor, how can you feel whether it has become larger or smaller?

This is simply out of line!

Lin Xiao shrugged and said, "You build a microscopic structure of yttrium barium copper oxide in your mind, and then simulate its electrons, and then deduce the effect of electron flow after pressurization, and you can feel it."

Chen Xun: "..."

He silently tried it in his mind, but there are more than ten molecules in a yttrium barium copper oxide unit cell to form a conductor, at least a few more unit cells should be made?

In that way, the amount of calculations in the brain will increase.

So in the end, Chen Xun chose to give up, and then complained: "My head is a human brain, not a computer."

Lin Xiao couldn't help shaking his head and laughing, obviously Chen Xun was complaining that his head was like a computer.

But this may be true. At least, Lin Xiao now feels that his brain is like a computer, and it is multi-core and multi-threaded, because he has been able to do five things at once.

He even felt that if he did more training, it might be possible to concentrate on all tasks. Of course, the problem of thinking should not be too complicated, but things like building molecular structure models and simulating electron flow directly in his mind , is still quite possible.

However, he didn't bother with this issue, and then said: "Okay, in fact, this is not a key issue."

"Key question?" Chen Xun looked puzzled.

"You said, what determines the critical current density?"

"Maximum Carrier Throughput."

"Well, the BCS theory told us that the carriers in low-temperature superconductors are Cooper pairs, so what about high-temperature superconductors?"

Chen Xun shook his head, "I can't say anything about that."

After all, this is also a point of debate in academic circles.

Lin Xiao smiled mysteriously, without explaining, but said: "First apply for the patent of this new type of yttrium-barium-copper-oxygen. During this time, I will write a thesis."

Although there are still some doubts, but after Lin Xiao said so, Chen Xun nodded and said, "I'll go to them to apply."

This kind of superconducting material with an improved critical current density must be patented.

Chen Xun took a look at the current that Lin Xiao had tested so far, and it even reached [-] amperes. Such a current has reached the level of niobium-titanium alloy.

As long as you apply for a patent, you will definitely be able to make some money in the future. Although it cannot be made into a flexible wire, it can still be used.

As for the thesis that Lin Xiao was going to write, it was probably about the properties of this new structure, YBCO, so Chen Xun didn't ask any more questions, and then left the laboratory.

But Lin Xiao continued to look at the yttrium-barium-copper-oxygen alloy in front of him, thinking in his heart.

He calculated it at the Institute of Physics more than a month ago. The reason why the critical current density of the transformed yttrium barium copper oxide can be increased is because more electron pairs suspected to be Cooper pairs appear.

However, he is still not sure whether these electron pairs are true Cooper pairs.

This made him start to diverge his thinking.

"First of all, why can it be superconducting under high pressure?"

On October 2020, 10, several scientists in the United States used extremely sophisticated experimental equipment to achieve superconductivity at 15 degrees Celsius at a temperature of 267Gpa.

The superconducting material they use is carbon-containing hydrogen sulfide.

But something like hydrogen sulfide is a gas at room temperature. How does a gas test superconductivity?

This is because the pressure of 267Gpa is equivalent to exerting a gravity of 26.7 tons on one square millimeter, and then directly compressing the gas into a solid.

There is obviously no difference between becoming a solid and solidifying at a low temperature, so high-voltage superconductivity and low-temperature superconductivity are essentially the same.

So Lin Xiao quickly passed this idea in his mind.

But then, his eyes suddenly flashed.

"By the way! Landau's Fermi liquid theory!"

"In the current academic circle, the understanding of strongly correlated physics beyond the framework of Landau's Fermi liquid theory is still at the stage of scratches."

"The mechanism of high-temperature superconductivity must be the strong correlation between electrons and fermions."

"According to the framework of Landau theory, as long as the perturbation theory converges, the interacting fermion system will behave qualitatively consistent with the non-interacting system..."

"If you substitute the situation of yttrium barium copper oxide into it..."

In Lin Xiao's brain, countless inspirations emerged like an explosion.

But all these inspirations eventually converge on one question.

"The perturbative divergence is not accompanied by a spontaneous symmetry breaking, but instead forms a highly correlated quantum liquid state—a non-Fermi liquid state."

"So, what is a non-Fermi liquid?"

Lin Xiao frowned, recalling all the documents and theories he had read.

"The current academic community only clarifies what is a Fermi liquid, but it only explains what a non-Fermi liquid is, and any Fermion model that is not a Fermi liquid is a non-Fermi liquid. What is it specifically? It's still foggy..."

Lin Xiao suddenly had a feeling that the high-temperature superconducting mechanism was hidden between the similarities and differences between the non-Fermi liquid and the Fermi liquid.

He scratched his head, and the feeling came again.

The more you pursue why, the more you enter into deeper problems, and this often means more and more trouble.

But he had to continue.

Sighing helplessly, he suddenly asked in his heart: "System, how many truth points do we need to exchange for that room temperature superconductor?"

System: "485 truth points are needed."

It is equivalent to saying that I have only completed 15 truth points of work after more than a month of hard work.

"Well, it's at least 3% progress, keep going."

As long as it takes another 33.33 times more than a month, he will have spent 500 truth points for nothing.

Well, thinking about it this way, I really didn't lose anything.

After comforting himself, he returned to his office and decided to finish the thesis first. As for Landau's Fermi liquid theory, let's wait until he has published the thesis.

……

In this way, time passed quietly again.

The days have come to the end of December, entering the academic world at the end of the year, but there is no change at all. At most, most Westerners temporarily put down their jobs and start celebrating Christmas.

However, two top international journals, "Nature" and "Physical Review Letters", successively published their last articles of this year, and they each had two articles, which caused a shock in the superconducting world.

"In the superconducting process of yttrium barium copper oxide, is it still because of a suspected Cooper pair of electrons that plays a role?"

This theory, which shocked superconducting physicists, appeared in front of them without any precautions or concerns.

Then, these superconducting physicists stopped thinking about taking a break at the end of the year, rushed into the laboratory, and started their experiments.

(End of this chapter)