Fermi noodles... What is it?
Scientific explanation: The Fermi surface is the isoenviron of the highest occupying energy level, which is the sub-interface between the occupied and non-occupied states of electrons when T = 0. In general, semiconductors and insulators do not use Fermi surfaces. And the concept of price with the top. The free electrons in metals satisfy the Pauli incompatibility principle, and their probability of distribution on a single particle energy level follows the Fermi statistical distribution. As a very important "surface" of solid materials, it determines whether it is light-transmitting, conductive and other physical properties. Due to the existence of the energy gap, semiconductors and superconductors themselves do not have this "face", and if this "face" can be produced, it will greatly change its nature.
Foreword to Science: Topological Superconductors Abroad
Earlier, an international team of scientists from Switzerland, the United Kingdom and China issued a statement saying they had discovered a new topological superconductor that would create more powerful and advanced quantum computers in the future. It is well known that superconductors can conduct electricity without resistance when cooled to a certain state. Superconductors exhibit their quantum properties compared to ordinary objects, which makes them very promising in quantum computers, which take advantage of the properties of quantum physics to process and store large amounts of data.
It is for this reason that the largest and most advanced IT companies are constantly working on the development of superconductors and using industrial quantum computers for superconductors. Currently, the "Achilles heel" of modern quantum computers is qubits, or rather, they are extremely sensitive to any external influence (electromagnetic influences, heat, collisions with air particles).
Therefore, engineers believe that only by creating stable qubits by using special topological conductors will it be possible to cope with this efficient sensitivity to provide the required protective performance. Just a few years ago, scientists had acquired materials such as bismuth selenium and bismuth tellurium semiconductors. But in order to fully implement quantum devices, it is necessary to implement topological materials with superconducting properties, not just on the surface. Over the course of numerous experiments, an international team of scientists managed to discover a new topological superconductor, LaPt3P. According to the scientists' findings, LaPt3P has great potential in the field of quantum computing. His findings suggest that further studies of mesons are generally important.
Experiments and conjectures about Fermi noodles
In 1965, the theorist Fulle theory predicted a path to achieve a special "segmented Fermi surface" in superconductors. But for more than 50 years, it has never been confirmed. In a study published in Science on October 29, Zhu Shuo, postdoctoral fellows of the School of Physics and Astronomy of Shanghai Jiao Tong University and the Li Zhengdao Research Institute, professors Zheng Hao, Jia Jinfeng and other collaborators successfully generated and detected segmented fermi surfaces caused by Cooper's momentum in the Bi2Te3/NbSe2 system using a low-temperature strong magnetic field scanning tunneling microscope.
In 1911, scientists discovered that superconductors, because of their strange properties such as zero-resistance conductivity and complete anti-magnetism, have become a long-standing research topic in physics. However, natural superconductors do not have Fermi noodles.
In 1965, Fulde theoretically predicted a special "segmented Fermi surface" in which a special "segmented Fermi surface" could be produced when the momentum of the Cooper pair in the superconductor was large enough to produce quasiparticles in the superconducting energy gap, resulting in a special "segmented Fermi surface". But the prophecy has never been confirmed. Because, for ordinary superconductors, if the Cooper pair is moved by increasing the current, when the Cooper pair has a certain degree of momentum and produces quasiparticles, the Cooper pair is also "disassembled", thus losing superconductivity. In other words, before the Fermi surface is produced, the superconductor has been "scrapped". Therefore, in order to realize the manual regulation of the superconductor fermi surface, the premise is to ensure that the "lizi" of its superconductivity is not lost, and the Fermi surface is generated.
To this end, the researchers hope to take advantage of the peculiarities of topological insulator/superconductor heterojunctions to solve this experimental puzzle. First, they used molecular beam epitaxial technology to precisely grow a 4-layer thick topological insulator Bi2Te3 film on the surface of the superconductor NbSe2. In this way, through the proximity effect of NbSe2, superconductivity is induced in topological insulators that are not originally superconducting.
But this requires that the film must be thin enough, otherwise the proximity effect will be very weak. "Molecular beam epitaxial technology can achieve precise control of the atomic layer, so it is the best means." Zheng Hao said... The induced superconductivity is more fragile than the intrinsic superconductivity, and the key to the experiment is to take advantage of this difference by applying a supercurrent to the induced superconductor and letting the current enter the topological insulator Bi2Te3 to achieve the strength of the superconductor to produce the fermi surface, but this strength is just within the controllable range of not destroying the superconductivity of NbSe2. That is to say, in the Bi2Te3/NbSe2 system, due to the large Fermi velocity of the surface state of the Bi2Te3 film, when the Cooper pair momentum in the NbSe2 superconductor is still very small, the Cooper pair in the Surface State of the Bi2Te3 film is already large enough to produce quasiparticles and achieve a segmented Fermi surface. In this way, the researchers cleverly solved the experimental difficulty of performing the test of Fulle prophecy.
However, to confirm the existence of such segmented Fermi surfaces, precise detection methods are also needed. At present, the more commonly used method for detecting Fermi surfaces in the world is angle-resolved photoelectron spectroscopy, but because the detection needs to be in an extremely low temperature environment, this method is not easy to achieve.
To do this, the researchers probed using a scanning tunneling microscope equipped with a dilution chiller and a three-dimensional vector strong magnetic field. They used a small horizontal magnetic field to generate a small superconducting current on the surface of the NbSe2 superconductor, and found that as the magnetic field increased, the momentum of the superconductor Cooper pair also increased, and more and more quasiparticles in the superconducting energy gap were also increasing, indicating that a segmented Fermi surface was gradually generated in the superconductor. For further verification, the researchers used quasiparticle interference techniques to detect standing waves in real space and confirmed the generation of Fermi planes through the Fourier transform.
Long-term accumulation of science
In fact, more than 10 years ago, the research team developed this topological insulator/superconductor heterojunction material system. This is a topological superconducting material on which researchers observed a Majorana zero-energy module that can be used in topological quantum computing. With the development of theory and technology, they explored the horizontal magnetic field and found an unusually sensitive response. For the research team, verifying theoretical predictions is only the first step. Since the direction and size of the magnetic field were found in the study to adjust the shape and size of the Fermi surface, regulate the topology, and construct a new topological superconductivity, they hope to further explore which physical properties of the superconductor it can change in the next experiment.
(The content of the article comes from the Internet)
Ex-story summary: High temperature superconductor - service China maglev
The resistance of a high-temperature superconductor is approximately 0. The resulting induced current will circulate in the superconductor, and the magnetic field generated by the induced current will be opposite to the direction of the orbital magnetic field, and will interact to produce a levitation force.
The working principle of high-temperature superconducting maglev: In the external magnetic field, the unique strong nailing ability of high-temperature superconductors makes it difficult for magnetic field lines to escape the shackles of the nailing center (for magnetic field lines that have been captured) and difficult to penetrate into the superconductor (for uncaptured free magnetic field lines). This unique peg characteristic allows the superconductor to induce superconducting currents that hinder this change as the external magnetic field changes. This electromagnetic interaction of the superconducting current with the external magnetic field creates a suspension force that is macroscopically balanced with the gravity of the suspension itself and provides the guiding force required for lateral stability.
Unlike conventional conductors, high-temperature superconductors have an approximate resistance of 0. The resulting induced current will circulate in the superconductor, and the magnetic field generated by the induced current will be opposite to the direction of the orbital magnetic field, and will interact to produce a levitation force. Due to the principle of "inductive electricity", neither the on-board suspension system nor the track needs to be powered.
According to the expert introduction: after the train is suspended, to maintain the suspension state, the only thing needed is liquid nitrogen, liquid nitrogen makes the superconducting material has been in a superconducting working state, and 78% of the air is nitrogen, so the cost of liquid nitrogen is low, but also energy saving and environmental protection. The high-temperature superconducting maglev also has a significant feature - the magnetic resistance of the train forward direction is almost 0, all of which make the ultra-high-speed application suitable for future traffic; the world's first high-temperature superconducting high-speed maglev prototype and test line that successfully rolled off the production line, the maximum test speed can reach 400 km / h, the target speed will reach 620 km / h, and the research on high-temperature superconducting maglev dynamics, aerodynamics, vibration, noise and other aspects can be carried out. As a major country in the world's high-speed rail, China's technology, equipment, construction and operation have reached the international advanced level.
In fact, the so-called "high-temperature superconductor" refers to a superconductor with a critical temperature of 40 K (about minus 233 degrees Celsius). In addition to maglev, superconducting materials are also used in many fields. At present, low-temperature superconducting materials have been commercially used, mainly in the field of nuclear magnetic resonance in medicine.
Superconducting technology is known as the 21st century power industry high-tech reserves, can effectively solve the current energy, transportation and other issues, now at home and abroad are studying the application of high-voltage line transmission of high-temperature superconducting cables, used in a variety of equipment superconducting motors, etc. And superconducting motors are light in weight, small size, in the wind turbine has special advantages, so the superconducting motor for wind power generation is also the current research hotspot. At the same time, superconductivity can be widely used in all electricity-related fields, such as information, detection, transportation, power technology, etc., and has important research and development value. At present, China is vigorously carrying out research on the preparation of superconducting materials and their applications. Continuously exploring superconductors with higher critical temperatures and strengthening the research of low-temperature refrigeration technology and cryogenic systems, which are closely related to the application of superconducting technology, is an important development direction in the future.
Understand a little technology every day and feel the difference in life
Itex glove box
Protector of scientific experiments