walk into unscientific

Chapter 835: Long time no see, Xiao Niu (finale)

"Another idea"

Hearing what Xu Yun said.

Zhou Guangzhao, Xue Qikun and others in the audience did not show much change in their expressions, except for a hint of thoughtfulness.

Just as Xu Yun said.

Just as we must mention gravity when talking about Mavericks, we must mention the BCS theory when it comes to the concept of superconductivity.

in the original history.

Ever since Onnes first discovered superconductivity in 1911, it has been believed that superconducting materials have the same properties as ordinary materials except that they have zero electrical resistance.

However, the discovery in 1933 that superconductors have perfect diamagnetism broke this concept. The perfect diamagnetism of superconductors is also called the Meissner effect.

By 1935.

The London brothers developed the London equations, which relate the current through a superconductor to the electromagnetic fields in and around it, thereby constructing a phenomenological theory of the electromagnetic properties of superconductors.

This theory predicted the existence of electromagnetic penetration depth, which was experimentally confirmed in 1939.

Then in 1950, physicists discovered that mercury isotopes with lower atomic weights transform into superconductors at slightly higher temperatures.
This suggests that theories of superconductivity must take into account that free electrons in a crystal are affected by lattice vibrations, a phenomenon known as the "isotope effect" of superconductivity.

Another three years passed.

Through the analysis of the thermal conductivity of superconductors, physicists realized that the energy distribution of free electrons in superconductors is not uniform, but has an energy gap.

However, all these theories are only used to explain the relationship between observed experimental phenomena, and do not explain these phenomena based on the basic laws of physics.

For nearly 50 years after Onnes discovered superconductivity, theoretical physicists had not developed a basic theory of superconductivity.

until
1957 years.

In this year, American physicists Bardeen, Cooper and Schrieffer proposed the famous BCS theory.

At that time, Schrieffer, Bardeen and Cooper discovered that electrons in superconductors would combine into Cooper pairs, and the movements of all electron Cooper pairs were interrelated and formed a whole due to the phonon-electron interaction.

So they began to think about how to describe the behavior of all Cooper pairs at the same time, rather than describing each Cooper pair individually.

These electron pairs are not affected by other electrons and the crystal lattice, which allows them to move unhindered.

Finally, at the beginning of this year, Bardeen and his students Cooper and Schrieffer combined these factors and published a short paper entitled "Microscopic Theory of Superconductivity."

In the article "Superconductivity Theory" published in December of the same year, they proved that the superconducting phase transition is a secondary phase transition. Their theory can explain the isotope effect and the Meissner effect, as well as why the superconducting state can only occur near absolute zero:

Under large amounts of thermal disturbance, the fragile Cooper pairs can break apart.

In addition, they also gave theoretical calculations on specific heat and electromagnetic penetration depth.

Ever since.

The BCS theory of superconductivity was constructed.

The establishment of the BCS theory was the first time in the history of physics that the superconductivity phenomenon was comprehensively and integratedly explained from a microscopic perspective, and it was impeccable both in theory and experiment.

In 1972, Bardeen, Cooper and Schrieffer won the Nobel Prize in Physics for proposing the BCS theory.

But just like Newtonian mechanics is a complement to classical physics, but somewhat weak in the microscopic field, the BCS theory soon encountered a bottleneck:
This theory can perfectly explain low-temperature superconductivity, but when it comes to high-temperature superconductivity, there are many unexplained situations.

Therefore, the physics community has also proposed many candidate mechanisms. The more popular ones are the RVB (resonant valence bond) theory, the tJ model and the spin fluctuation model.

These theories each have advantages and disadvantages, and all need to be tested by experimental evidence.

"The RVB theory holds that the electrons in copper-oxygen high-temperature superconductors form resonant valence bonds on the copper-oxygen planes, which are strong quantum entanglement rather than Cooper pairs. This valence bond can cross different copper-oxygen planes, leading to superconductivity."

Xu Yun then turned to the next page of the PPT and gave a sharp review of several existing theories:

"The RVB theory can explain some strongly correlated effects of high-temperature superconductors, such as pseudogap and antiferromagnetic order, but its drawback is that it does not provide a specific electron pairing mechanism and symmetry, nor does it provide measurable predictions."

"The earlier tJ model believed that electrons formed Cooper pairs on the copper-oxygen surface by exchanging spin-1/2 excitons, which could explain the d-wave symmetry and charge-spin separation of high-temperature superconductors, but also did not give a specific pairing mechanism."

"The spin fluctuation model assumes that electrons form Cooper pairs by exchanging spin fluctuations. In this framework, spin fluctuations are quasiparticles generated by the coupling of antiferromagnetic order and charge density waves."

"The spin fluctuation model can also explain the d-wave symmetry and strong correlation effects in high-temperature superconductors, but unfortunately, it still does not provide a specific pairing mechanism."

"Student Xu Yun."

After Xu Yun finished speaking, Academician Xue Qikun raised his hand to interrupt him:
"From what you said, it seems that the approach you adopted this time is not the mainstream one?"

"Yes."

Xu Yun nodded, confirming Xue Qikun's judgment:

"The theory I used to describe the mechanism has never been proposed before. I call it the Chern-Xu magnetic vector potential canonical theory."

This time.

Including Mr. Yang who had remained silent, everyone in the audience was stunned.

Chern-Xu canonical theory of magnetic vector potential.

These few simple words seem to contain a lot of information.
For example, magnetic vector potential.

Compared with electric current and charge, the physical quantity of magnetic vector potential may be less well-known.

In fact, it is a chirality vector, which is related to the magnetic field:
It is known that the divergence of vector B is zero in a stable magnetic field. According to the important vector identity, the divergence of the curl of any vector field is always zero. Therefore, B can be expressed as B=▽×A. The vector field A becomes the vector magnetic potential, so the current distribution A is obtained. By differentiating A, B can be obtained.

Simplifying ▽×▽×A=μJ, we can get ▽^2A=-μJ, which is the vector Poisson's equation, which is equivalent to three scalar Poisson's equations in the rectangular coordinate system.

Very simple and easy to understand.

This thing is related to high-temperature superconductivity, because electrons moving in an electromagnetic field are always accompanied by a phase, which is actually the magnetic vector potential.

"."

Then, Mr. Wang, who was sitting next to Xue Qikun, thought for a moment and asked Xu Yun:

"Xiao Xu, please go on and explain your theory in detail."

Seeing this, Xu Yun nodded again. This time he did not use PPT. Instead, he picked up the chalk and wrote on the blackboard beside him:

"In a sense, superconductivity is like passing the parcel, and the electrons are like children. The children sit still in their seats, so they don't collide with each other and generate resistance, and the parcel they pass is the massless phase."

"So starting from this idea, we can write a gauge-invariant Hamiltonian under the tight-binding model, which is UHU=∑ijtijcieiAijcj+h, where Aij=θiθj."

"When electrons jump to the left or right, they will have a positive or negative phase, which is the main source of superconducting current. If we calculate the change of the local electron number ni=cici over time, that is, the Heisenberg equation, and the continuity equation nt+Jx=0, it is easy to get the current operator."

"Below the critical temperature, the electrons pair up to form copper pairs and condense into the bcs ground state - up to this step, the BCS theory still holds true."

“Then my next idea is.”

Speaking of it.

Xu Yun paused deliberately:
"Use the Fermi surface structure approximation for the energy gap function of superconductors." (See Chapter 449, another foreshadowing that spans 400 chapters)

mentioned earlier.

The so-called Fermi surface actually refers to the equienergy surface of momentum space.

The Fermi surface was first defined in an ideal non-interacting Fermi gas system, and later extended to the electron model. In recent years, it has become common in the field of solid materials.

Its essence is the movement of free electrons in a three-dimensional infinite potential well. The electrons correspond to λ=h/p, so a standing wave is formed in the conductor.

Then, based on the definition of the wave vector, the wave vector value of the standing wave in which a single electron is located can be determined.

Da da da.
Xu Yun took the chalk and quickly wrote down lines of equations on the blackboard, while the big guys below the stage became visibly more serious.

Xu Yun’s ideas in this part are very clever. Generally speaking, after condensing to the bcs ground state, what remains is the discussion of the macroscopic quantum state.

That is, the wave function of a large number of electrons with disorderly phase distribution forms a wave function with a certain phase due to spontaneous symmetry breaking.

It's like durian.

In most people's general understanding, the way to eat durian is to eat it raw after opening the shell.

But Xu Yun took a different approach this time and chose to roast the durian.

And what’s interesting is that.
While grilling, Xue Qikun suddenly discovered that this method seemed to be quite delicious?

“It is known that when the variable x in the power series is allowed to take complex values, the values ​​to which the power series converges form a two-dimensional region in the complex plane.”

“然后利用高斯函数的Fourier变换 F{ea2t2}(k)=πaeπ2k2/a2，以及Poisson求和公式可以得到”

"Consider the integral g(s) = 12πi∮γzs1ez1dz, where the contour should be limk→∞gk(s) = g(s)"

Xu Yun quickly wrote down his previous derivation process on the blackboard, and Xue Qikun and others' eyes became brighter and brighter.

One of the experimental difficulties in high-temperature superconductivity research is the strongly correlated electron effect, that is, the interaction between electrons cannot be simply ignored or considered approximately, and magnetic and electrical interactions are equally important.

For example, the energy gap function of conventional superconductors is generally an isotropic s-wave, but for copper oxide superconductors it is an anisotropic d-wave, and the energy gap function of iron-based superconductors is mainly s±-wave.

However, after Xu Yun did this, the controversy could be resolved at least from a mathematical perspective.

Xu Yun's transformation changes the phase of the occupied state relative to the empty state at each lattice point, that is, cj→UcjU=eiθjcj.

Under the appearance of a single quantization, this is equivalent to changing the phase of the local wave function of a single particle.

In other words.

The transformed model has the structure of a tensor product, cannot mix the state spaces of different lattices, and does not mix occupied states and empty states.

This leaves only the infinite number of unitary transformations to consider.

From the spin perspective associated with the Jordan-Wigner transformation, only two or three loops meet the requirements.
This is a brand new matching mechanism, and it is not as simple as local matching.
Suddenly.

薛其坤院士又想到了去年7月12日，中科院在《自然》发表的那篇有关液氮温区镍氧化物超导体的论文。（/doi.org/10.1038/s41586-023-06408-7）

This is the second type of unconventional superconductor family that scientists have discovered after cuprates that can break through the liquid nitrogen temperature (36 K) after 77 years. This type of superconductor has a corresponding magnetic field-suppressed superconducting transition phenomenon and linear resistance behavior in the normal state.

The intuitive factor leading to this phenomenon is that the +2.5 valence of the Ni ion plays a unique role. Its two different d orbitals affect the correlated electronic states in the c direction and within the ab plane respectively. Doesn’t the mechanism fit the deduction used by Xu Yun?
And at this moment.

Xu Yun's writing on the blackboard continued.

"One of the most surprising universal properties of high-temperature superconductivity is the juxtaposition of superconducting and antiferromagnetic phases. The antiferromagnetic exchange coupling coefficient J is responsible for the half-filled antiferromagnetic phase, and the same coupling coefficient can also lead to the formation of spin singlets, which is a prerequisite for superconductivity."

"In my theory, the antiferromagnetic phase is characterized by a three-dimensional order parameter Na, the so-called staggered magnetization, which has the characteristics of spin 1, charge 0 and total momentum (π, π)."

"On the other hand, a spin-singlet d-wave superconducting phase is characterized by a complex order parameter Δ with two real components, which has spin 0, charge ±2 and total momentum 0"

"My idea is to combine these five components into a single object, called a superspin na = (ReΔ, Nx, Ny, Nz, ImΔ), which transforms the antiferromagnetic phase into a superconducting phase and vice versa."

"These quantum numbers uniquely determine the form of the operator up to a factor of form. One of them is given by π = ∑ k (cosk x cosky) ck + π, ↑ ck, ↑. Since this operator has spin 1, we can obviously define three operators π α."

"The most direct evidence for this part of the deduction comes from the neutron scattering resonance peaks below Tc of the YBCO superconductor. These resonances have spin 1, momentum (π, π), and resolution-limited peaks at 92meV, 67meV, and 52meV for materials with Tc=41K, Tc=33K, and Tc=25K, respectively. The corresponding data are on page 243 of the paper."

The stipulated time for Xu Yun's defense was one hour, but it took Xu Yun more than five hours from the beginning of writing on the blackboard to the completion of his entire presentation.

But neither the judges nor Academician Pan urged Xu Yun. In the end, a condensed matter physics expert like Academician Xue Qikun couldn't help but walk to the front of the stage and start a discussion with Xu Yun on the spot.

The only people who were dissatisfied with Xu Yun during the whole process were probably the medical care experts outside the venue.

Especially those health care assistants who were about the same age as Xu Yun, when they thought that they would probably have to take care of this old man when Xu Yun was in his sixties, they instantly felt that their lives were dark.
that's it.

At 5:13 pm.

Having used up all nine pieces of chalk, Xu Yun took a deep breath and wrote the last line:

"The mechanism of high-temperature superconductivity has been proven. The person who proved it is Xu Yun."

"."

Looking at the densely written words on the blackboard in front of them, the judges all looked somewhat puzzled.

Especially Mr. Yang, Mr. Wang and Zhou Guangzhao, although they looked tired, their eyes were shining brightly.

It is true that they took the initiative to support Xu Yun this time, but precisely because of this reason, they actually had very high expectations for Xu Yun.

Even to Mr. Yang and other parties involved, this request seemed a bit unreasonable.

Unexpectedly, Xu Yun gave them such a big surprise. This was actually a high-temperature superconductor!

True.

It would be difficult for Xu Yun to win the Nobel Prize based solely on this theoretical deduction, but this is only a temporary situation.

If someone can fully prove Xu Yun's theory through physical phenomena in the future, then the Nobel Prize will definitely be in Xu Yun's pocket.

Not an exaggeration.

Even if Xu Yun does not produce any results in the future, his position in the history of physics will not be lower than the top 200.

If we add an adjective to filter, then Xu Yun can even be said to be the most accomplished person in the world, and no "peer" can compare with him!
more importantly.
Xu Yun is only 24 years old now!
A 24-year-old young man can solve the mechanism problem of high-temperature superconductivity. Where will his end be?

Landau's second gear?
Comparable to Mr. Yang?
The undisputed most accomplished Asian physicist?

Comparable to Niu Ai?

Or.
Fly higher?

When he thought of this, Zhou Guangzhao, who was already 95 years old, began to beat faster again.

At his position and age, there is nothing more satisfying than seeing the successor of the Chinese physics community.
Zhou Guangzhao even thought of his good friend Yu Min, who also created a miracle in the history of Chinese scientific research at a young age.

Well?
Suddenly.

For some reason, a strange picture suddenly popped up in Zhou Guangzhao's mind:

Dayu was sitting at his desk, writing furiously, while someone beside him was handing him a towel and pouring him some water.

The man's face was a little blurry, but he vaguely resembled Xu Yun.
It’s strange, why did such an idea come to my mind?

Then Zhou Guangzhao shook his head vigorously and put this inexplicable thought behind him.

Then he took a deep breath and asked Xu Yun:

"Xiao Xu, is there a more accurate name for this mechanism?"

"The Chern-Xu magnetic vector potential canonical theory you used earlier seems a bit vague or mathematical."

Mr. Wang and Mr. Yang on the side also nodded.

There are quite a few physical theories that sound mathematical in their names, but when it comes to high-end mechanisms, their mathematical nature makes them seem a bit cheap or lack physical persuasiveness.

"Have."

Xu Yun looked up at him and said slowly:

"The Chen Jingrun-Xu Yun theory involves two vectors, two superspinners and a singlet, so I also call it the .2 theory."

Chen Jingrun-Xu Yun circle theory?

221 theory?

Zhou Guangzhao was silent for a few seconds, and it was unclear what he was thinking. Finally, he nodded slightly:
"Good name."

all in all.

At this point, the rest of the process is simple.

The five judges made their defense decisions in front of the camera equipment and unanimously gave Xu Yun excellent evaluations, and he passed the defense on the spot.

At this point, Xu Yun is also a glorious master's degree recipient.
Afterwards, Xu Yun chatted with a few more bigwigs, and considering that it was getting late, he took the initiative to say goodbye and left the meeting room.

After accepting the congratulations from Lu Chaoyang and Gu Qunqing who were waiting at the door, Xu Yun posted a message on Weibo and Moments, then returned to the small room in the guesthouse, saying that he was a little tired.

After locking the door.

Xu Yun went straight into the halo space.

At this moment, there are still three light gates standing in the space, two of which are newly refreshed copies with unknown contents.

The remaining one is the light gate that Xu Yun had only completed the novice mission and has yet to be reopened.

The world behind the light gate is in 1665 AD, also
Where it all began.

"."

Coming to the light gate, Xu Yun closed his eyes and took a deep breath.

Then he reached out and unscrewed the handle of the light gate.

Swah——

After a slight feeling of dizziness.

The environment around Xu Yun quietly changed to a noisy and primitive town, with Grantham's church, a small shed selling ketchup, and
He was grinning with a smile on his face, and even the lentil strands on his back teeth were clearly visible. He was "thawing" from the time-stop state.
Isaac Newton.

"Long time no see, Maverick."

End of the book

Note:
Throw flowers at the end, and thank you all for your company along the way. I’d like to bow to you all here!

Thank you all for your support over the past period of time. The performance of this book is not the best, but what makes me emotional is not the performance, but the fact that a small unknown person like me can meet "little candles" like you.

Don't rush to delete your bookshelf. When there are extra chapters or new books released, I will notify you in this book. I will recover my health as soon as possible. You may not believe it, but I have already thought of the ending of the new book.
In addition, there are full subscription groups and alliance leader groups that you can join. You can come in and chat, and you will be notified when new books are released.

　Finally, I recommend a book by a friend, "I Landed in the Primordial World in the World of Cultivation"

　　
　
(End of this chapter)