Chapter 835 Long time no see, Mavericks (finale)
"Another idea"
Hearing what Xu Yun said.
The expressions of Zhou Guangzhao, Xue Qikun and others in the audience did not change much, but showed a little thoughtfulness.
Just as Xu Yun said.
Just like when mentioning Mavericks, one must mention gravity, when it comes to the concept of superconductivity, one must mention BCS theory.
in the original history.
Since Onnes first discovered the phenomenon of superconductivity in 1911, it has been believed that superconducting materials have the same properties as ordinary materials except for zero resistance.
However, the discovery in 1933 that superconductors were completely diamagnetic broke this concept. The complete diamagnetism of superconductors was also called the Meissner effect.
By 1935.
The London brothers developed the London equation, which related the current passing through a superconductor to the electromagnetic fields within and around it, thus constructing a phenomenological theory about the electromagnetic properties of superconductors.
This theory predicted the existence of electromagnetic penetration depth and was experimentally confirmed in 1939.
Then in 1950, physicists discovered that mercury isotopes with lower atomic weights have slightly higher temperatures when they transform into superconductors.
This suggests that theories of superconductivity must take into account that free electrons in crystals are affected by lattice vibrations, a phenomenon known as the "isotope effect" of superconductivity.
Another three years passed.
By analyzing 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 interrelationships between observed experimental phenomena and do not explain these phenomena based on the basic laws of physics.
In the nearly 50 years since Onnes discovered the phenomenon of superconductivity, theoretical physicists have not developed a basic theory of superconductivity.
Until
1957.
In this year, American physicists Bardeen, Cooper and Schriever proposed the famous BCS theory.
At that time, Schriever, Bardeen, and Cooper discovered that electrons in superconductors would combine into Cooper pairs. The motions of all electron Cooper pairs were related to each other and formed a whole due to the phonon-electron interaction.
So they started thinking about how to describe the behavior of all Cooper pairs simultaneously, rather than describing each Cooper pair individually.
These electron pairs are unaffected by other electrons and the crystal lattice, which allows them to move unhindered.
Finally, early that year, Bardeen and his students Cooper and Schriever combined these factors and published a short paper titled "The Microscopic Theory of Superconductivity."
In the article "Superconducting Theory" in December of the same year, they proved that the superconducting phase transition is a second-order phase transition. Their theory can explain the isotope effect and the Meissner effect, and why the superconducting state can only occur near absolute zero. ：
Under large thermal perturbations, fragile Cooper pairs can break.
In addition, they present theoretical calculations on specific heat and electromagnetic penetration depth.
Ever since.
The BCS theory of superconductivity was constructed.
The establishment of the BCS theory is the first time in the history of physics that the superconducting phenomenon is comprehensively and comprehensively explained from a microscopic perspective, and it is impeccable in theory and experiment.
In 1972, Bardeen, Cooper and Schriever won the Nobel Prize in Physics for proposing the BCS theory.
But just as Newtonian mechanics supports classical physics but is somewhat weak in the microscopic field, BCS theory soon encountered a bottleneck:
This theory can perfectly explain low-temperature superconductivity, but there are many unexplained situations when it comes to high-temperature superconductivity.
Therefore, the physics community has also proposed many candidate mechanisms. Currently, the more popular ones are RVB (resonance valence bond) theory, t-J model and spin fluctuation model.
Each of these theories has advantages and disadvantages, and all have yet to be tested with experimental evidence.
"RVB theory holds that the electrons in the copper-oxide high-temperature superconductor form a resonant valence bond on the copper-oxide surface, which is a strong quantum entanglement rather than a Cooper pair. This valence bond can span different copper-oxide surfaces and lead to superconductivity. .”
Xu Yun then turned to the next page of the PPT and made critical comments on several existing theories:
"RVB theory can explain some strong correlation effects of high-temperature superconductivity, such as pseudogap and antiferromagnetic order, but its drawback is that it does not give specific electron pairing mechanisms and symmetry, nor does it give measurable predictions. ”
"The earlier t-J model believed that electrons formed Cooper pairs by exchanging excitons with spin 1/2 on the copper-oxygen surface, which can explain the d-wave symmetry and charge spin separation of high-temperature superconductors, but it also did not give Come up with a specific pairing mechanism.”
"The spin fluctuation model believes that electrons form Cooper pairs by exchanging spin fluctuations. In this framework, spin fluctuations are a quasi-particle produced by the coupling of antiferromagnetic order and charge density waves."< br>
"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 give a specific pairing mechanism."
"Classmate Xu Yun."
After Xu Yun finished speaking, Academician Xue Qikun raised his hand and interrupted him:
"From what you say, the idea you adopted this time does not seem to be one of the mainstream ones?"
"That's right."
Xu Yun nodded and confirmed Xue Qikun's judgment:
"The theory I used to describe the mechanism this time has not been proposed before. I call it the Chen-Xu magnetic vector potential canonical theory."
This time.
Including Mr. Yang, who had been silent, everyone in the audience was suddenly stunned.
Chen-Xu magnetic vector potential canonical theory.
A few simple words seem to contain a lot of information.
For example, magnetic vector potential.
Compared with current charge, the physical quantity of magnetic vector potential may be less well-known.
In fact, it is a rotational vector, related to the magnetic field:
It is known that the divergence of the vector B in a stable magnetic field is zero. According to the important loss identity, the divergence of the curl of any vector field is always zero. Therefore, B can be expressed as B=▽×A, and the vector field A becomes the vector magnetic potential. , so the current distribution A is obtained, and B can be obtained by differential operation on A.
Simplifying ▽×▽×A=μJ, we can get ▽^2A=-μJ, which is the vector Poisson equation, which is equivalent to three scalar Poisson equations in the Cartesian coordinate system.
Very simple and easy to understand.
This thing also has a certain relationship with 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 while and asked Xu Yun:
"Xiao Xu, go ahead 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:
"In a sense, superconductivity is like passing flowers by beating a drum, and electrons are like children. The children sit in their own seats and do not move, so they do not collide with each other and generate resistance. The flowers they pass on are the massless phase."
"So starting from this idea, we can write a gauge-invariant Hamiltonian under the tight binding model, that is, UHU=∑ijtijcieiAijcj+h where Aij=θiθj."
"When electrons jump to the left and right, there will be a positive and negative phase attached. This is the main source of superconducting current. If you calculate the change of the local electron number ni=cici over time, it is the Heisenberg equation, and continuity The equation nt+Jx=0, it is easy to get the stream operator."
"Below the critical temperature, electrons pair up to form a copperpair and condense to the bcs ground state - up to this step, the BCS theory is still valid."
"Then my next thought is."
Speaking of which.
Xu Yun paused deliberately:
"Approximating the Fermi surface structure of the energy gap function of superconductors." (See Chapter 449, another foreshadowing that spans Chapter 400)
Mentioned earlier.
The so-called Fermi surface actually refers to the equal energy surface of momentum space.
The Fermi surface was first defined in the ideal non-interactive Fermi gas system, and was later extended to electronic models. In recent years, it is commonly used 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 according to the definition of 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 quickly wrote down a line of calculations on the blackboard with a piece of chalk, while the big guys in the audience became visibly serious.
Xu Yun's thinking in this part is very spiritual. Generally speaking, after condensing to the bcs ground state, the rest is the discussion of macroscopic quantum states.
That is to say, the wave function of a large number of electronic phases that are chaotically distributed forms a wave function with a certain phase due to spontaneous symmetry breaking.
It's like durian.
In most people's conventional understanding, the eating process of durian is to open the shell and eat it raw.
But Xu Yun took a different approach at this time and chose grilled durian.
And what’s very interesting is.
As he was roasting, Xue Qikun suddenly discovered that his method seemed quite delicious?
"It is known that when the variable x in the power series is allowed to take complex values, the convergent value of the power series forms a two-dimensional region on the complex plane."
"Then using the Fourier transformation of the Gaussian function F{ea2t2}(k)=πaeπ2k2/a2 and the Poisson summation formula can be obtained"
"Consider the integral g(s)=12πi∮γzs1ez1dz, where the circumference should be limk→∞gk(s)=g(s)"
Xu Yun quickly wrote his previous derivation process on the blackboard, and Xue Qikun and others' eyes became brighter and brighter.
One of the experimental dilemmas in high-temperature superconductivity research is the strongly correlated electron effect, that is, the electron-electron interaction cannot be simply ignored or approximately considered, and magnetic and electrical interactions are equally important.
For example, the energy gap function of conventional superconductors is generally isotropic s-wave, but when it comes to cuprate superconductors, it is anisotropic d-wave. The energy gap function of iron-based superconductors is mainly s± wave.
However, after Xu Yun made such a move, at least from a mathematical perspective, this controversy can be mixed together.
Xu Yun's transformation changes the phase of the occupied state relative to the empty state at each grid point, that is, cj→UcjU=eiθjcj,.
Under the appearance of primary quantization, this is equivalent to changing the phase of the local wave function of a single particle.
In other words.
The transformed model has a tensor product structure, cannot mix state spaces of different grid points, and will not mix occupied states and empty states.
As a result, there are only a few unitary transformations left to consider.
From the spin perspective associated with the Jordan-Wigner transformation, there are only two or three loops that meet the conditions
This is a brand new pairing mechanism, and it is not as simple as local matching.
Suddenly.
Academician Xue Qikun thought of the paper on nickel oxide superconductors in the liquid nitrogen temperature zone published by the Chinese Academy of Sciences in Nature on July 12 last year. (/doi.org/10.1038/s41586-023-06408-7)
This is the second type of unconventional superconducting family discovered by scientists after 36 years after copper oxide that breaks through the liquid nitrogen temperature (77K). This type of superconductor has a corresponding magnetic field that inhibits the superconducting transition phenomenon and Normal linear resistive behavior.
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 associated electronic states in the c direction and the ab plane respectively. However, the mechanism is not consistent with the derivation used by Xu Yun. ?
And at this moment.
Xu Yun's writing on the blackboard continued.
"One of the most amazing universal properties of high-temperature superconductivity is the adjacency between the superconducting and antiferromagnetic phases. The antiferromagnetic exchange coupling coefficient J is responsible for the half-full antiferromagnetic phase, and the same Coupling coefficients can also lead to the formation of spin singlets, which are a prerequisite for superconductivity. ”
"In my theory, the antiferromagnetic phase is characterized by a three-dimensional order parameter Nα, the so-called staggered magnetization, so it 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 one object, called superspin na = (ReΔ, Nx, Ny, Nz, ImΔ), transforming the antiferromagnetic phase into the superconducting phase or vice versa."
"These quantum numbers uniquely determine the form of this operator at a level that differs by a form factor. One of them is given by π=∑k(coskxcosky)ck+π,↑ck,↑. Because this operator has spin 1. We can obviously define three operators πα."
"The most direct evidence for this part of the derivation comes from the neutron scattering resonance peaks under the YBCO superconductor Tc. These resonances have spin 1, momentum (π, π), and the response to Tc=92K, Tc=67K and Tc=52K The materials are located at the resolution limit peaks of 41meV, 33meV and 25meV respectively, and the corresponding data are on page 243 of the paper."
The allotted 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 all the explanations.
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 come to 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 and health experts outside the venue.
Especially those health care assistants who are about the same age as Xu Yun, when they think that Xu Yun will most likely have to take care of this old man when he is in his sixties, they instantly feel that life is dark.
that's all.
At 5:13 p.m.
Xu Yun, who had used up all nine pieces of chalk, took a deep breath and wrote the last line:
"The mechanism of high-temperature superconductivity has been proved. The certifier is Xu Yun."
"."
Looking at the dense blackboards in front of them, the expressions of several judges were a little confused.
Especially Mr. Yang, Mr. Wang and Zhou Guangzhao, although their faces looked tired, their eyes had a bright brilliance.
It is true that they took the initiative to support Xu Yun this time, but precisely for this reason, their requirements for Xu Yun are actually very high.
Even in the eyes of Mr. Yang and other parties involved, this request is a bit too much.
Unexpectedly, Xu Yun gave them such a big surprise. This was a high-temperature superconductor!
True.
Simply relying on this theoretical derivation, it would be difficult for Xu Yun to win the Nobel Prize, but this is only a temporary situation.
If someone can completely prove Xu Yun's theory through physical phenomena in the future, then the Nobel Prize will definitely belong to Xu Yun.
Not an exaggeration.
Even if Xu Yun produces no results in the future, his status in the history of physics will not be lower than the top 200.
If we add another attribute to filter, then Xu Yun can even be said to be the most accomplished tweeter in the world. 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 problem of the mechanism of high-temperature superconductivity. Where will his end be?
Landau's second gear?
Comparable to Mr. Yang?
Undisputedly the most accomplished Asian physicist?
As much love as a cow?
Still say.
Fly higher?
When he thought of this, the 95-year-old Zhou Guangzhao's heart beat faster again.
At his status and age, there is nothing more satisfying and satisfying than seeing the successors of the Chinese physics community again.
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.
Huh?
Suddenly.
For some reason, a strange picture suddenly appeared in Zhou Guangzhao's mind:
Yu Yu was sitting at the desk writing furiously, and someone beside him was handing him a towel and pouring water.
The man's face was a little blurry, but there was a faint shadow of Xu Yun.
It's strange, why did I come up with such an idea?
Then Zhou Guangzhao shook his head vigorously, throwing this inexplicable thought to the back of his mind.
Then he took a deep breath and asked Xu Yun:
"Xiao Xu, does this mechanism have a more accurate name?"
"The Chen-Xu magnetic vector potential canonical theory you used before seems a bit vague or mathematical."
Wang Lao and Yang Lao on the side also nodded.
There are many physical theories with mathematical names, but when it comes to high-end mechanisms, the mathematical characteristics will make them a little "priceless" or lack physical convincingness.
"Yes."
Xu Yun looked up at him and said slowly:
"The Chen Jingrun-Xu Yun Weidao theory involves two vectors, two superspinors and a single state, so I also call it the .221 theory."
Chen Jingrun-Xu Yun Weidao theory?
221 theory?
Zhou Guangzhao was silent for a few seconds, unable to tell what he was thinking, and finally nodded slightly:
"Good name."
all in all.
Once things have reached this point, the rest of the process is simple.
The five judges made their defense decision in front of the camera equipment, unanimously gave Xu Yun an excellent evaluation, and passed the defense on the spot.
At this point, Xu Yun is also a glorious master's degree recipient
Xu Yun then chatted with several big guys for a while, and considering that it was already late, he took the initiative to say goodbye and left the conference room.
After accepting the congratulations from Lu Chaoyang and Gu Qunqing who were waiting at the door, Xu Yun conveniently posted a message on Weibo and WeChat Moments, and returned to the small room of the guest house on the grounds that he was a little tired.
After locking the door.
Xu Yun went straight into the halo space.
At this time, there are still three light gates erected in the space, two of which are newly refreshed copies with unknown content.
The remaining one is the light gate that Xu Yun has only completed the novice mission and has yet to be reopened.
The world behind the Light Gate is 1665 AD, which is also
Where it all began.
"."
Arriving at the light door, Xu Yun closed his eyes and took a deep breath.
Then he stretched out his hand and unscrewed the handle of the light door.
Swish——
After a slight dizziness.
The environment around Xu Yun quietly changed to a noisy and primitive village. Surrounded by Grantham's church, a small shed with ketchup, and
With a big grin on his face, even the lentil threads on his back molars are clearly visible, and he is "thawing" from the time-stopped state
Isaac Newton.
"Long time no see, Maverick."
Complete book
Note:
After scattering flowers, I thank you all for accompanying me along the way. The fisherman is here to bow to you!
Thank you all for your support during the past period. The results of this book are not top-notch, but what makes me sigh is not the results, but that a little transparent person like me can meet "little candles" like you.
Don’t be in a hurry to delete your bookshelf. When there are extra chapters and new books are released, they will be notified in this book. I will take care of myself as soon as possible. You may not believe it when I tell you, but the ending of the new book has already been planned.
In addition, there are full subscription groups and leader groups that you can join. You can come in and chat, and we will also notify you of new book releases
Finally, I recommend a book by a friend, "I Landed in the Ancient World of Immortal Cultivation"
(End of chapter)