A breakthrough by an Israeli researcher may help decipher the secret of superconductors, while overcoming a major problem in science
In 1911, the Dutch physicist Heike Kamerlingh Onnes studied the properties of solid mercury at a very low temperature (about 269 degrees below zero, i.e. - only about four degrees above absolute zero) and discovered an amazing purpose. The electrical resistance of the mercury has completely disappeared. That is, if you connect such a mercury ring to a current source, and then disconnect, the current can continue to move through the mercury indefinitely. Kamerling-Ones immediately understood the enormous importance of the discovery and called the special state of mercury "superconductivity". He hurried to investigate whether the phenomenon existed in other metals, and soon discovered it in tin and lead as well. The discovery made waves in the entire scientific world (and earned Kamerling-Ons the Nobel Prize in 1913) - it was the first time a "perfect" system was discovered - one in which there is apparently no loss of energy. Such conductors may change the face of electrical systems and electrical devices, and since they do not heat up (there is no loss of energy), they can be used in many applications that require an extremely strong electric current and are therefore prone to heating up, and also for creating extremely strong magnetic fields (an electric wire through which a current is carried creates a field magnetic). Later, researchers discovered another interesting property of superconductors - they repel a magnetic field applied to them. This means that if you force a magnet closer to such a conductor, at a certain point it will float above the conductor. It is also possible to design the magnet so that it moves over the conductor without contact or friction between them, which results in huge energy savings.
Cold, but less so
There was one big thorn in the great wall of superconductivity. The phenomenon exists only at temperatures close to absolute zero (-273.15 degrees). Therefore, the use of its wonderful properties is extremely cumbersome and expensive, and in many cases - not practical. More precisely, this has been the case for 75 years. In 1986, two researchers at IBM laboratories announced a revolutionary discovery - ceramic materials based on copper, which maintain properties of superconductors even at relatively high temperatures. Johannes Bednorz and Karl Müller discovered a material that functioned as a superconductor at a temperature of 35 degrees Kelvin (above absolute zero), and already a year later a material was discovered that maintained this property at 92 degrees Kelvin (-181 Celsius). It is still very cold, but that temperature can already be achieved using liquid nitrogen, a material much more readily available than the liquid helium needed for temperatures approaching absolute zero. In recent years, superconductors have also been discovered at 135 Kelvin, a relatively high temperature, but still very far from the dream of physicists and engineers - a material that will be a superconductor at room temperature and will change our world from end to end. One of the obstacles on the way to realizing this dream is the obstacle of knowledge - scientists still do not fully understand the phenomenon of superconductivity and how it occurs, especially at high temperatures. Scientists estimate that the phenomenon is related to changes in the magnetic properties of the material, but attempts to decipher the mystery, mainly in this direction, encountered an insurmountable obstacle, in the form of the sign problem.
Not everything is positive
The sign problem is one of the most challenging problems facing scientists. It arises in systems where it is necessary to summarize billions of data, some negative and some positive, and in many cases complex numbers are also involved, i.e. the root of a negative number. In such problems, because of the summation of positive and negative, any small error in the scheme can lead to a large deviation in the result, and in the absence of a mathematical way to reduce the margin of error, it is very difficult to refer to the results. The sign problem is particularly common in issues related to quantum physics, especially those in which it is necessary to calculate and sum trajectories of many electrons or particles similar to them. For example - when trying to understand in depth phenomena such as changing magnetism in a material. However, the problem is not limited to this area. It is at the root of many problems considered unsolvable in particle physics, nuclear physics and condensed matter physics, and is also considered a very central problem in computer science. A general solution to the sign problem - if it exists - will yield real breakthroughs in these fields, and will most likely win the solver a Nobel Prize.
A private solution
As mentioned, it is very possible that there is no general solution to the sign problem, but a breakthrough by an Israeli researcher makes it possible to deal with the problem - or at least successfully circumvent it - in the issue concerning the magnetic properties of superconductors. Dr. Erez Berg, currently a researcher in the Department of Condensed Matter Physics at the Weizmann Institute, did the research during his post-doctoral training at Harvard University. He relied on a model that allows sampling a relatively small number of electron trajectories, instead of trying to sum up all the billions of trajectories, and processed the model so that it can only be used for trajectories with a positive sign, which - of course - there is no problem in summing up accurately. In a complex theoretical work, he developed with his colleagues a computer program that enables the sampling to be performed with the necessary level of precision, and to try to see how the electrons will behave in a superconductor at a high temperature. The result was very surprising "We saw that the metal becomes a superconductor exactly where the change of its magnetic phase takes place", says Dr. Berg. "This allows us to try to better understand how superconductors work at high temperature - we now need to draw, with the help of the software we developed, predictions of how certain materials will behave and examine whether the magnetic changes are indeed the key to superconductivity at high temperature." The breakthrough was recently published in the important journal Science. Now, says Berg, the research is going in two directions. The first is an examination of the issue of superconductivity. If it turns out that magnetic changes are the basis of the phenomenon, it will be possible to try to test the development of superconductors at higher temperatures, the dream of course being materials that hardly require cooling. The other direction is to check if the solution developed for this particular case can be applied to other physical issues whose solution is stuck because of the sign problem. Berg's development may not be suitable for additional problems, but experience proves that if one problem is successfully solved, there is probably a solution hidden somewhere for at least some of its sisters, and thus the door was opened to deal with a problem that until now was considered insoluble.
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It's like eternal life
How beautiful it is like a dynamo that doesn't end in a superconductor, the current circulates in an electric circuit without interruption, this could be a solution to the end of my electricity bill at home lol and even today people install solar collectors but there is something to it
To download the original article free of charge (in science you pay), please contact the website
http://arxiv.org/abs/1206.0742
and download pdf.
For those who are able to read an article in theoretical physics of condensed matter.
Otherwise the article in Hidan does an excellent service in the simplicity of presenting the material.
Inaccurate intuitive explanation (pays attention to intuition in analogies and less on formality):
In a superconductor in a quasi-classical interpretation (ie obeys Newton's laws) which is not true - because the effect is quantum,
There are no collisions of the charge carriers with the oppositely marked ions that trap them, or they do not waste energy, because of the low temp. Why? At the Kharta level: because at low temp the particles lose their identity and if they change energetic roles there is no difference because they are all low energy. There is complete synchronization between the particles carrying the motion like a dense collection of people dancing in circles in a crowded room, which because of the low temperature (= energy) do not collide with each other or with people standing in the way, but only rotate in (electrical) circles at a fixed distance from each other.
The sign is in my opinion only a sign of angular momentum, spin, which is a property of fermions, particles that at higher temps cannot occupy the same energy level. If we liken the energy levels to empty boxes that a particle can fall into, fermions cannot sit in two boxes with the same energy.
Example of fermions: electrons and ions.
In contrast, bosons - particles that can sit in two boxes with the same energy level and even more.
An example of bosons: photons - light particles = the energy carriers of the electromagnetic field.
The subject of superconductivity is currently treated by a theory called Fermi Liquid Theory, and he developed it
Originally Lev-Davidovitz and Landau in the 30s and 40s, for the superfluidity of helium used to cool nuclear reactors. Landau, despite being free in his statements, was rescued from a detention camp during Stalin's days because the chief scientist in the Russian atomic project jumped and said to Stalin, I can't do without him. Today, statistical physics has developed to unbelievable theoretical levels. Suffice it to mention the ability to describe phase transitions, and the Ising model.
What did Landau innovate? Before him, multi-electron problems in quantum physics were handled by writing a multi-particle Schrödinger equation, which is almost unsolvable, and unsolvable. In his method there is a multi-particle quantum model that combines
Classical statistics but on quantum particles.
Are there explanations in Hebrew about the sign problem?
I found only articles in English…
Beautiful apps Emmanuel
If you already mentioned then:
1. An end to the permanent waste of several tens of percent of the electricity that flows through the metal cables on the electricity poles from the power plant to the end consumer. (Well, here the one who will enjoy it is probably only the electric company;) )
2. Cheaper (and better) MRI devices, resulting in increased access to these important devices (cryogenic cooling will not be needed, and better because stronger magnetic fields can be produced).
Eli you asked and answered in the same sentence
A magnetic field can produce work and indeed it produces energy if it changes near a conductor
If the magnetic field is constant and does not change then no work is created and therefore there is no contradiction here
Just like a stretched spring as long as the spring does not change its length there is no work
The reason superconductors excite the imagination is the many applications that can be produced
for example
Magnets a million times stronger than existing magnets without wasting energy (hovering trains)
Electromagnetic bearings with friction coefficients 0
The company that will succeed in producing a superconductor at normal temperatures will dominate all applications that have bearings or moving parts (go and think)
As soon as it becomes a superconductor at normal temperatures, you can forget about large chemical batteries
It will be possible to easily store energy and release it 1000 times faster than in batteries
To me, as far as I understand, a material in a superconducting phase is a perfect antiferromagnet. That is, in the presence of an external magnetic field, edge currents are created in it, and the electron spin states in it line up to create a magnetic field opposite to the external field and thus to screen the external field inside the material.
There is no input of energy into the system here. The system changes its properties in the way I described, to stay in an energetically preferred state. That is, a state with a lower total energy than, for example, a state in which the material is not magnetic.
Also, when you invest energy and flow current in the system (and immediately disconnect the wire that conducts current to the system), current flows through the conductor without losses, and as long as the superconducting phase is maintained, the current will continue to flow and therefore create a permanent magnetic field.
When producing work from this, it is equivalent to using a material that is a permanent magnet. After all, in a permanent magnet there is no reduction in magnetism over time.
This is how, for example, the Maglev works in China. It is a rail paved with electromagnets, while the train that hovers above the rail contains a permanent superconducting magnet at the bottom. The movement of the train is achieved by inducing a magnetic field that changes cyclically and is like a kind of wave that pushes the train forward.
Just to get an idea of how lossless the superconducting phase is, I'll give an example that I know personally.
Today, low-temperature superconductors are widely used to produce extremely strong magnetic fields. For example, in the particle accelerator at Sarn and in various laboratories around the world.
I am familiar with such a use in the field of nuclear magnetic resonance (NMR), where a constant and strong magnetic field is needed. In such NMR devices there is a superconducting material that is well isolated from the environment and preserved by using liquid helium at a temperature of about 4 degrees Kelvin. When the device is installed, a current is passed through it to produce the necessary magnetic field and then it is isolated from the environment.
In the same case that I am familiar with, it is a device like this that was installed in 1996, and from then until today it flows exactly (!) the same current that was put into it, without energy losses!
Their current in a conductor creates a magnetic field that can create work, which means it's a waste of energy. So how is there no waste of energy in a superconductor?