Chapter 834 A defense that will go down in history (Part 2)
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In the conference room.
Looking at the title of the paper in front of him, Academician Xue Qikun subconsciously made a somewhat funny move:
He slowly took off his glasses, rubbed his eyes hard with his knuckles twice, and then looked at the paper with wide eyes again.
Then
Well, there is still no change in that line:
"Discussion on the mechanism of high-temperature superconductivity".
See this situation.
Bang bang bang——
Academician Xue Qikun's big heart, which had not fluctuated much when he won the Buckley Award, started beating violently in an instant.
In this day and age, the concept of superconductivity is not unfamiliar to many people.
Physically, superconductivity is a phenomenon in which the resistance of a material becomes 0 when it is below a certain temperature. The transformed material is called a superconductor.
Anyone who has been to high school should know this.
In a circuit, charges in a wire are driven by a voltage and move like a runner, creating an electric current, but the resistance across the conductor impedes their movement.
If the circuit is made of superconductors, charges can run freely in the circuit and current will continue to flow.
In a loop made of superconducting lead, the current could go months without any sign of weakening.
The phenomenon of superconductivity was first discovered by Onness in 1911. He used liquid helium to cool mercury and found that the resistance of mercury became zero at -268.98°C, thus opening the door to the world of superconductivity.
From a business and technology perspective.
Once superconducting materials can be applied, human science and technology will usher in a new leap forward.
For example, in the field of power transmission, home appliances, and transportation - at that time, the wheels of all moving objects can be removed.
At that time, the Formula One racing championship will be replaced by the low-altitude hover car race in "Star Wars". You can drive hover cars and hover boats to reach every corner of the world.
But unfortunately, the ideal is very full, and the reality is very skinny.
Until now, the practical applications of superconductors have mainly been concentrated in specific situations such as particle accelerators, magnetic levitation, and superconducting quantum interferometers.
In terms of power engineering, especially the long-distance power transmission of superconducting wires, which have high hopes, large-scale application is still far away.
And what limits the wide-scale application of superconductors?
There is only one root cause:
temperature.
The temperature at which a material transforms into a superconductor is called the superconducting critical temperature (Tc). Only below this Tc can a superconductor maintain its superconducting properties.
However, the Tc of most materials is very low, basically below -220°C, and requires the use of liquid nitrogen or liquid helium to maintain a low-temperature environment.
Picture this.
You have worked so hard to build a superconducting transmission line that is hundreds of kilometers long, and it also needs to be immersed in liquid nitrogen for cooling. The cost is so exaggerated.
Therefore, in order for superconductors to be more widely used, it is necessary to find materials with a higher Tc that can maintain superconducting properties, preferably at room temperature (about 25°C).
Since the discovery of superconductivity, physicists have never stopped searching for high-Tc superconductors, but they have always struggled.
In the first 70 years since the discovery of superconductivity, it was difficult for the upper limit of Tc to even exceed -240°C.
Fortunately, later physicists gradually discovered superconductors with Tc exceeding -173°C. The current record holder for the highest critical temperature of a superconductor is hydrogen sulfide at 1.5 million atmospheres. The Tc is about -73°C, which is still a certain distance from the ideal room temperature. , such high-pressure conditions also mean that it is difficult to apply in practice.
at the same time.
Based on the above concepts, superconducting materials have extended two small branches:
Room temperature superconductivity and high temperature superconductivity.
In general.
We call superconductors with a critical temperature higher than 40K high-temperature superconductors, and superconductors with a critical temperature higher than about 300K are called room-temperature superconductors.
In other words, in the superconducting world, "room temperature" is actually much higher than "high temperature".
What’s even more special is.
Until now, the physics community has still not concluded the complete mechanism of high-temperature superconductivity.
This is a black hole in the field of condensed matter physics. Today, it is recognized that there are only two unsolvable problems in condensed matter physics:
One is a strongly correlated system, and the other is the complete mechanism of high-temperature superconductivity. (Note: There are also some views that regard the two as one problem, which is the same as whether cherries and cherries are the same species. It depends on how you look at it)
In addition, even the fractional quantum Hall effect, which Academician Xue Qikun specializes in, can only be regarded as a classic problem, not a dead end.
True.
Since this mechanism is extremely close to the theoretical level, it is actually not very possible to win the Nobel Prize by relying on it alone. However, for practitioners in the physics community, unraveling this mechanism is no less meaningful than winning the Nobel Prize.
Nowadays, there are many teams engaged in mechanism derivation at home and abroad. Even Academician Xue Qikun has two research groups promoting this topic. One of the leaders of the project team is Yangtze River and the other is an outstanding young scientist.
The result was unexpected.
Academician Xue Qikun actually saw such an earth-shattering title at Xu Yun's master's defense?
Is Xu Yun deliberately brushing aside the situation and finally playing an ambiguous word game?
Or did he really pick up this pearl of condensed matter physics?
"Mr. Zhou, Mr. Zhou!"
Just when Academician Xue Qikun was inexplicably shocked, a burst of urgent sound suddenly came from a communication device on the desktop where Academician Zhou Guangzhao was sitting:
"Mr. Zhou, your heartbeat has just exceeded 100! The data of Mr. Yang and Mr. Wang are also very high!"
"Is something going on? Do we need a health care team to come in?"
Mentioned earlier.
At this time, three of the seven people in the room (including Xu Yun) were close to or over 100 years old. The youngest of the three, Zhou Guangzhao, was 95 years old.
Therefore, in order to ensure the safety of several national treasures, the Academy of Sciences prepared a medical team in advance to conduct real-time monitoring off-site through equipment worn by several big shots.
Just now, the doctor in charge of health care suddenly discovered an anomaly:
The heart rates of several big guys began to rise at the same time. Among them, Academician Zhou Guangzhao's value even jumped from 57 to a peak of 102 per minute, which scared the doctors in the health care team and their heart rates also soared to 180+
"I'm fine."
Just as the leader of the medical team was wondering whether to pick up the medical kit and rush into the room, Zhou Guangzhao spoke to the communication device:
“I just saw some unexpected content, so there’s no need to come in.”
"Mr. Yang and Xi Ji are both fine. We are both conscious. If we really feel unwell, I will inform you."
The person on the other side of the communication device was silent for a while, and finally sighed helplessly:
".Received."
As experts who specialize in providing medical care to these seniors in the scientific research community, the members of the medical team naturally know the tempers of these little old men.
Although they are usually happy and cheerful, when they encounter academic matters, they become very stubborn and cannot be persuaded no matter how hard they try.
On the contrary, those veteran cadres who have retired from the political circle will be more cooperative with the medical team. This is probably the difference between top liberal arts students and science students.
After hanging up the communication device.
Academician Zhou Guangzhao leaned back slightly, took Xu Yun's paper in front of him with both hands and looked at it a few more times, then raised his head and looked at Xu Yun:
"Classmate Xu Yun, are you serious about this title?"
Looking at Zhou Guangzhao's slightly scrutinizing gaze, Xu Yun suddenly felt a somewhat complicated emotion in his heart.
In the dungeon, Xu Yun and Zhou Guangzhao could not be said to be friends who exchanged lives for their lives. At least they could be said to be revolutionary comrades who lived together day and night. They worked together to complete many arduous tasks. However, in reality, Mr. Zhou had never met him before. Bai Dian said in a slightly questioning tone.
Comrades in the copy, strangers in reality.
The so-called misalignment of time and space is probably this feeling
However, this emotion was only fleeting in Xu Yun's heart, and he soon adjusted his state:
"Hello, Academician Zhou, I am honored that you can participate in my graduation defense. I can generally understand some of your thoughts - after all, this topic may involve a relatively high level and is not something that a master's degree can touch. .”
"But on the other hand, from my personal point of view, this master's defense is also an important life node that cannot be missed. I have no reason to ruin this defense."
"So to put it bluntly, I am quite confident in the quality of the content of this paper."
When Xu Yun spoke, his posture was very low, but his expression was not too restrained. He answered Zhou Guangzhao's questions in a tactful but firm manner.
After all, it's exactly what he said.
The paper he wrote is not just a headline, nor is it an ambiguous rubbish, but a clear explanation of the complete mechanism of high-temperature superconductivity.
"."
Zhou Guangzhao was silent for a while after hearing this, turned his head and looked at Xue Qikun, and said to Xu Yun:
"In that case, classmate Xu Yun, you can start your defense."
Seeing this, Xu Yun nodded, walked from the side of the podium to the center of the podium, quickly scanned the scene, and said:
"Hello, fellow reviewers, I am today's respondent Xu Yun. I am 24 years old and a graduate student. My student number is 114514"
"The content of my defense today is "Discussion on the Mechanism of High-Temperature Superconductivity", a very hot and controversial topic in the field of condensed matter."
Xu Yun paused as he spoke, then pressed the remote control pen, and the image of Xu Yun's thesis was quickly projected on the projector:
"High-temperature superconductivity generally refers to superconductors with a superconducting critical temperature above 40K, which is a concept relative to low-temperature superconductors such as mercury and lead, which have a critical temperature of about 10K."
"As for applications, it usually refers to copper oxide ceramic superconductors such as YBaCuO and HgBaCaCuO. Their superconducting critical temperature is around 100K, which is higher than the concept."
"The phenomenon of superconductivity was first discovered by Onnes in 1911. Then in 1957, 44 years after the discovery of superconductivity, three scientists, Bardeen, Cooper and Schrieffer, proposed the famous BCS theory, which satisfactorily explained the phenomena of Hg and Pb. The phenomenon of superconductivity in superconductors - for which they won the Nobel Prize in Physics in 1972. ”
"BCS theory can well explain some properties of low-temperature superconductors, such as energy gaps, Meissner effects, and isotope effects. However, many phenomena that violate BCS theory have been found in high-temperature superconductors, such as pseudo-gaps, linear resistance, and electric charges. Spin separation, strong superconducting phase fluctuations, etc."
"This shows that there are strongly correlated electronic systems in high-temperature superconductors that are difficult to deal with using perturbation theory or mean fields."
"Therefore, I abandoned the framework of BCS theory in my paper and adopted another idea to explain high-temperature superconductivity."
Note:
Tomorrow's finale will be a big chapter. My hands are shaking a little when I write this sentence. The book will be released on November 26, 2021. It has been two and a half years. Thank you for accompanying me all the way. (End of chapter)