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outline of superconductivity

In 1911, in Leiden, the Netherlands, starts the history of superconductivity. The Dutch physicist Heike Kamerlingh Onnes dedicated his work to investigate low-temperature rare gases. I discovered how to get liquid, and referred its investigation to know the variations of resistivity as the material approached absolute zero. He knew even then that many materials had a linear decrease of resistivity with the temperature, but it was not happened when the temperature approaches 0 K.

Heike Kamerlingh Onnes

The solution found Hg cooling to temperatures near 0 K. Chose mercury because after several distillations can be considered almost completely pure without relative difficulty of preparation. HK Onnes observed that the resistivity completely disappeared around 4K. He had discovered the superconductividad.HK Onnes received the Nobel Prize in Physics for his research on low temperature materials two years later, in 1913.

In 1933, Walter Meissner and Robert Ochsenfeld discovered the "Meissner effect", which tells us that during his state superconducotr, a material repels the magnetic field.

Meissner Effect

Over the next few years, superconducting materials are discovered Uneven increasingly higher temperatures.

1941: Niobium nitride, superconducting at 16 K.

1953: Vanadium - Silicon superconductor at 17.5 K.

diamagnetism levitation for a clear example of the Meissner effect

1957: John Bardeen, Leon Cooper and John Schiefer agreed to develop the first theory on superconductivity. According to this, the electrons are grouped in pairs, called Cooper pairs, through the attractive force of an electron after the local polarization of the network of positive ions. It is known as BCS theory

1960-69: We develop a superconducting Niobium - Titanium for a particle accelerator in England. You can start looking here and the first applications of superconductivity to advanced technology industries.

1962: manufacturing a superconducting wire Niobium - Titanium for commercial use. Also this year, Brian D. Josephson predicted by Cambridge University that electric current can flow between two superconducting materials even when separated by an insulator or superconductor. Is what is known as "Josephson effect" or tunnels.

Tunneling

1972: John Bardeen, Leon Cooper and John Schiefer win the Nobel Prize in Physics for his theory BSC.

1980: Decade vital for research into superconductors. This same year the first organic superconductor synthesized by Klaus Bechgaard of the University of Copenhagen (and three French.) It must be cooled to 1.2K and bring to high pressure for the superconductivity. This possibility was suggested in 1964 by Bills Little of the University of Stamford.

1986: Alex Müller and Georg Bednorz of IBM Research Laboratory in Rüschlikon, Switzerland, developed a fragile ceramic component superconductor at 30 K. Was used, lanthanum, barium, copper and oxygen for the synthesis of this ceramic

1987: Researchers at the University of Alabama-Huntsville substitute for Lanthanum Yttrium in the molecule and Alex Müller Georg Bednorz reaching a critical temperature of 92K. YBaCuO

1993: The first synthesis of mercury-cuprates was developed at the University of Colorado and the team of A. Schilling, M. Cantoni, JD Guo and HR Ott of Switzerland. Until then it had reached a 138 Tc K. This material was obtained with thallium-doped, mercury-cuprate compressed elements mercury, thallium, barium, calcium, copper and oxygen.

1997: Researchers found that at temperatures near absolute zero of an alloy of gold and indium are superconducting and a natural magnet. However, the conventional wisdom supports a material with such properties may not exist since more than half a dozen of these components have been found.

section of superconducting wire

2005: Superconductors.ORG found that the increase in the weight ratio of the planes between layers of perovskites can increase the transition temperature Tc significantly. This allowed the discovery of at least 30 new high-temperature superconductors.

2008: March 6, 2008 found that the compound:

(SnPb 0.5 _In 0.5) Ba 4 Tm 5 _{Cu 7 O 20 +}

superconducting properties has about 185.6 Kelvin, which is the first superconductor material to "room temperature" (-87.4 º C).

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The Hebrides (photography)

"Beyond the windswept shores of this wild and sparsely populated islands, there is nothing left but the Atlantic Ocean to America" \u200b\u200b

(Click on each photo to enlarge it)

Skavaeg Loch, Isle of Skye

Wildflowers in spring

Stornoway Castle

Loch Ness, as shown by the Scottish landscape

Tintin in

Isla Negra, story that takes place in the Scottish islands

Norwick beach

Loch Dunvegan, Isle of Skye

William Wallace Monument

The harsh climate of the Hebrides

Corelle New Bread Plates

What is (and how) the superconductivity?

As we know, metals and alloys, the resistivity (the degree of difficulty encountered materials on the go) of the material increases with temperature, and decreases with it, almost linear. However, in superconductors at temperatures near absolute zero (0 K) there is a sudden drop in resistivity. The resistivity is then zero. Despite the zero resistivity, conductivity is not infinite (something mathematical formula deduced from conductivity).

That is, the ease being the conductivity of a material to the movement of electrons through it, superconductivity will occur when the electrons are not opposed to its passage through the conductor material (or just do it, is theoretically impossible to achieve a conductivity of 100%).

Superconductivity is therefore a property found in many metals and some ceramics, which appears at low temperatures, characterized by the loss of resistivity at a certain temperature characteristic of each material, called temperature critical.

Superconductors also have a marked diamagnetism, ie, they are repelled by magnetic fields. Which cause the levitation effect we see in the image:

Superconductor at temperatures near 0 K

On the other hand, we lack the explanation of how superconductors. There are two theories. One is the BCS theory, briefly explained in the first section of the paper, and one theory Ginzburg - Landau.

Figure Resistivity - temperature, where we see clearly the decline in the first low temperature in a superconductor.

Notice to mariners: the explanation of these theories do not simplify or for work, talking about really complicated concepts. If you read on, you risk not understand almost nothing about the writing. However, only two paragraphs, then return to discuss issues more "simple."

BCS theory tells us that "superconductivity can be explained as an application of Bose-Einstein condensate. However, the electrons are fermions , so that they can apply this theory directly. The idea is based on the BCS theory is that electrons are paired into a pair of fermions behaves like a boson . This pair is called a Cooper pair and the link is justified in the interactions of electrons with each other mediated by the crystal structure of the material. " As we can see, requires knowledge of quantum mechanics than would have like to know when assessing the application of Bose - Einstein conductivity at temperatures near 0 K. But by having a brief affair, and I quote his explanation and was done with the BCS theory, we say that "Bose-Einstein condensate is the aggregation of matter that occurs in certain materials at very low temperatures . The property that characterizes it is that a macroscopic number of particles of the material passed to the lowest energy level, called the ground state. The condensate is a quantum property that has no classical analogue . Due to the Pauli exclusion principle, only bosonic particles can have this state of aggregation. This means that the atoms are separated and form ions. A grouping of particles at that level is called Bose-Einstein condensate. "That is, the BCS theory is based on the application of Bose - Einstein on the conductivity and resistivity of a material.

Table periodic elements according to their superconductivity

The other theory, the Ginzburg - Landau, is much better at predicting the qualities if the materials to study are not homogeneous, since BCS theory only works when the energy band to study homogeneous. This theory tries to explain the phenomenon of macroscopic form based on the breaking of symmetries in the phase transition. "The theory is based on a variational calculation which attempts to minimize the Helmholtz free energy regarding the electron density found in the superconducting state. The conditions for applying the theory are

• temperatures have managed to be near the critical temperature, since it is based on a Taylor series expansion around T _c .
• The wave pseudofunción Ψ and the vector potential , must vary smoothly.

This theory predicts two characteristic lengths:

• penetration length is the distance that the magnetic field penetrates the superconductor material

• coherence length: is the approximate size of the Cooper pair "

We find also different classifications between superconductors. According to the theory that best explains them, are classified into conventional (explainable by the BCS theory) and unconventional (can not be explained by BCS theory or its derivatives).

I believe, however, that the classification more important for superconductors is that the divide in type I superconductors, which pass abruptly from the superconducting to normal and type II, which have an intermediate or mixed between the superconductor and normal.

Superconductivity is one of the fields of physics fascinating twentieth century . He belongs to that small group of scientific advances capable of changing the way of life of mankind. Its range of applications is broad, but includes essentially three types: the generation of strong magnetic fields, making driving cables electricity and electronics. The first type we use as spectacular as the manufacture of levitated mass transit systems, that is, trains that float above their tracks without having friction with them, making it possible to achieve speeds that develop airplanes. The second is the possibility of transmitting electricity from the production centers, such as dams or nuclear reactors to centers of consumption without any losses in transit. For the third type we may mention the possibility of manufacturing extremely fast supercomputers, or any electronic gadget with a range and capabilities far greater than today.

Certainly superconductor applications in almost any field of technology, but how do they work? How do we explain their behavior? At this point we will explain the key theoretical behavior of superconductors.

The use of superconductors, as mentioned before, allows the transmission of electrical energy without loss (or minimization) or the production of magnetic fields. It's where I want to focus now.

As you know, the LHC suffered numerous delays in its originally planned, even several months, due to cooling problems. These problems were due to that they could not maintain the low temperature superconductors low enough to operate at full capacity. Keep in mind that a superconducting temperature of one degree above the right can lead to considerable energy losses with all that that entails, not only economic losses but damage from the heat released in the rest of the system.

magnetic train in Shanghai, the "maglev"

With this example I set, we can see the main problem superconductors have today: the need to reach temperatures low enough to make them work.

Although these temperatures are considerably higher today than 100 years ago, when HK Onnes discovered superconductivity of mercury to 4 K, it remains expensive to achieve temperatures so low, about -100 º C in the most advanced compounds, to achieve superconductivity. That is why superconductivity is considered one of the fields of science, along with nuclear fusion, which can cause an industrial and technological revolution with the highest incidence in the world.

If nuclear fusion is not difficult to imagine why. A virtually inexhaustible energy source (operation is the same as the one with the Sun), relatively clean (there are contaminants, derived mainly from the need to maintain a temperature of more than 1 million degrees) and would have multiple applications.

In the case of superconductors, the application will be valid for any field of technology: improvements in power transmission and the elimination of losses as heat will make a global improvement of any system that works by electricity. Will also no doubt to improved performance in electric motors, or even as already used today in building magnetic levitation trains. That is, we help you make better energy we have, at lower cost, especially once it becomes a superconductor at room temperature so that we can achieve more efficient mills and even brand new they are unthinkable today.

NOTE: This entry is part of a work I did recently, as the next on the history of superconductivity. The language is more complicated than usual, although I have simplified and explained the terms "rare" as much as it has been possible.

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screens of the future, on sale in 2011 Returning to old habits

was recently awarded the Nobel Prize in Physics 2010 at two research University of Manchester, Andre Geim and Novoselov Konstantin. The reason for the award was that they had been isolated for the first time, a material that was supposed its existence but had not yet been created artificially: graphene. Formed by carbon atoms (as graphite, carbon or diamond), but whose structure is markedly different: they are arranged in a single sheet.

On the uses of graphene could write a book (probably has already, or will be): conductors or superconductors at low temperatures, body armor, ... Today we only use as screens.

But for starters, what is the graphene and what makes it so special?

Well, as we have said graphene is a material composed of carbon atoms arranged in a hexagon with one atom thick. It also presents some physical qualities that make it a unique material. Without going into theoretical physics, suffice to say that graphene is a semiconductor as we know of no other today. Or silicon, currently excellence semiconductor electronics industry (or industry in general) can be compared with the physical properties of graphene. Also presented. however, several drawbacks, especially as its use as a substitute for silicon is concerned. Even today we use it can have, we are only beginning to "know" the end of the day. Why

is supposed to be so special then its use as a screen? The truth is that not look anything like the screens that exist today. Infinitely thin LED or LCD screen, has a thickness of just one atom. This, along with flexibility, we offer the opportunity to save a screen in our pockets without any problems. A picture will explain this better than words:

Samsung is expected that the market the first screens of graphene in 2011. And this is only the beginning of a small revolution we live. Imagine that with a screen whose size can vary to your liking, you could keep in your pocket, you could read the newspaper, book, television or the internet anywhere. On a more simple, economical and comfortable than a mobile art ould do so. You could wrap the wrist and use it as a clock (also allow very precise measurement of weather conditions due to the sensitivity of graphene). For this, the truth is that there are not many years. According to specialists, at most ten years, and probably less.

To end this introductory material is expected to enable some progress recently in disitintos unthinkable areas of science and industry (some of these fields I am sure we can not even imagine yet), here a video we see exactly what we were talking about:

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too long since my last entry, and still not quite sure how, I again have time to update the blog. It was a shame not to anyone who deserved to spend the beginning of this journey, so it seems lucky to have again, as míniimo, loose times to continue this task.

confess that I lied before, actually I do know why now I have time to blog. Not only that is not in exam time and can keep up to date without being studies until 12 pm, also has influenced you've sent to hell in my browser the vast majority of sites you lost before the , already scarce, time spent online. So, in summary, I'm back, and hopefully this mosvez be for long. At least until January, I will not excuse examinations. I think this is promising.

Let's get to it.