Tag: Superconductivity

Room Temperature Superconducting materials could revolutionize our technology in so many ways but will scientists ever be able to discover one? Also, the end of James Holzhauer’s streak as Jeopardy champion.

Everybody knows that there are some materials, primarily metals, which are able to conduct electricity. At the same time there are other materials like rubber or plastic that are insulators and through which electricity cannot flow. However even the best conductors, such as copper or silver still have a small resistance. Because of this nearly half of all of the electrical power we produce is just eaten up by the resistance in the kilometers of wire that are needed to get electricity from a power plant to your home or office.

Half of all the E;ectrical energy we generate is simply lost in the resistance of the wires needed to transmit it! (Credit: T&D World)

That some materials can become ‘superconductive’, loosing absolutely all of their resistance has been known since physicist Heike Onnes first discovered the phenomenon in 1911. The problem was that the materials Onnes studied only became superconductive at ultra cold temperatures, within just a few degrees of absolute zero (minus 273ºC). Because of the expense of the equipment needed to cool the conducting material down to the low temperatures needed to initiate superconductivity for many years the phenomenon remained a curiosity, of no practical value.

Heike Onnes in his Lab (Credit: American Institute of Physics)

The potential uses of superconductivity are so great however that it’s not surprising that physicists kept looking, trying new materials in their search for a Room Temperature Superconductor (RTS). In fact there has been so much work carried out over the years that six Nobel Prizes have now been awarded for research into superconductivity starting with the one awarded to Onnes himself.

One breakthrough came in the 1980s with the discovery of ceramic conductors, technically known as cuprate-perovskite ceramics. These materials were found to become superconductive at temperatures higher than that of liquid nitrogen, minus 196ºC.

In the Meissner effect a superconducting material is repelled by a magnetic field (Credit: Extreme tech)

With that advance superconductive materials came into some limited technological use, primarily for the generation of powerful magnet fields such as those for Magnetic Resonance Imaging (MRI) scanners and magnetic levitation (Mag-Lev) in high-speed trains. These few uses of superconductivity have nevertheless become so economically valuable that they have increased the pace of research toward the discovery of superconducting materials that do not require any cooling at all.

Recently a new high temperature record has been set at the Argonne National Laboratory by a team of scientists from the University of Chicago. The new record is minus 23ºC, considerably higher than the temperature of ‘dry ice’ (solid Carbon Dioxide at minus 78.5ºC). A superconductor that only needs dry ice to cool it could greatly expand the industrial uses of the phenomenon.

Before you start buying stock in superconducting companies however I must tell you that the material, Lanthanum Hydride, formula LaH10 also requires a pressure of 270 Gigapascals or about 2 million atmospheres before it will exhibit superconductivity! In order to attain such a high pressure the tiny sample of material had to be squeezed between two diamond anvils.

X-Ray images of Lanthum Hydro have revealed the structure of the superconducting material (Credit: Drozdov et al)

If you’re thinking that 2 million atmospheres of pressure is a bigger technical problem than low temperature, well you have a point. However the researchers are hoping to find conditions under which the high pressure will initiate superconductivity but where superconductivity will remain once the pressure has been removed!

Whether the University of Chicago scientists succeed in their efforts or not the discovery of a material that is superconductive at temperatures that are commonly seen in the arctic regions of the World is still a major advance. With each step forward science learns a little bit more and perhaps one day soon superconductivity will become as familiar and widespread a property of our technology as semi-conductors are now.

 

Before I leave for today I would like to take a moment to mention the end of Jeopardy contestant James Holzhauer’s 32 game winning streak. Although Holzhauer only won about half as many games as the all time Jeopardy champ Ken Jennings did he still came within $60,000 of Jenning’s all time winnings of over $2.5 million!

James Holzhauer and his 32 game total Jeopardy winnings (Credit: Deadspin)

In other words Holzhauer’s per game winnings were about twice that of Jenning’s, which is what made James a very exciting player to watch. Whenever he got a ‘Daily Double’ he would often bet everything he had even if he already had a comfortable lead!

In the end Holzhauer was beaten by his own style of play. The new Jeopardy champion, Emma Boettcher was playing well but was still a bit behind Holzhauer when she got the last ‘Daily Double’. Following James’ example Boettcher bet everything she had and got the question right, taking a lead she never relinquished. To his credit James quickly congratulated Emma on her victory, indeed throughout his winning streak Holzhauer had often congratulated those opponents who had made him work for his wins!

The Start of James Holzhauer’s final game. Emma beat him! (Credit: IndieWire)

Now of course Jeopardy is just a game show, but at least it’s a game show that requires more than a bit of knowledge and intelligence. I think TV could use more shows like Jeopardy that appeal to our intelligence so I’m glad that James Holzhauer’s reign as Jeopardy champion succeeded in increasing the show’s ratings quite a bit. Hopefully the success of James, and Ken Jennings and Emma Boettcher will inspire a few producers in Hollywood to create a few more shows like Jeopardy for those of us who like to think!

New Developments in the Study of Superconductivity and what is a Superconductor anyway?

One of the earliest known scientific ‘Laws’ dealing with electricity is called Ohm’s law after it discoverer, Georg Simon Ohm. As usually stated Ohm’s law asserts that when an electric voltage is placed across an object it will cause an electric current to flow through the object and that the amount of current you get for a certain voltage is a property of the object called the resistance. In equation form:

V=I*R

Here voltage is V, current is I and resistance is R. In other words double the voltage and you get double the current through an object or one third the voltage will get you one third the current through the same object.

But even before Ohms time scientists knew that some materials, mainly metals, allowed a great deal of current to flow while other materials allow only a tiny current. In terms of Ohm’s law metals had a low resistance while most non-metals had a much higher resistance.

This is why we use metals like copper to conduct electricity and non-metals to insulate us from electricity. The range of possible resistances in different materials is enormous, the resistivity of glass for example is a million trillion time higher that of copper!

Scientists also soon learned that the resistance of metals depends on temperature with lower temperatures causing a drop in resistance. In 1911 the physicist Kamerlingh Onnes was trying to see how far this reduction in resistance would go when he discovered that the resistance of Mercury suddenly dropped to zero at a temperature of about 4 degrees Kelvin (about -270 degrees C).

Before long many elements were found to have similar critical temperatures where their resistance disappears, although it is a curious fact that the two best normal conductors, silver and copper, never become superconductive. The image below shows the familiar periodic table of the elements with those elements that have been found to go superconductive highlighted.

Periodic Table showing Superconducting Elements (Credit: Superconductors.Org)

Now in practical terms the use of superconductive materials in our electrical systems would be extremely valuable. This is because almost one half of all the electricity the human race produces just gets eaten up by the resistance in the wires getting to your house. (For example your toaster uses the resistance in its coils of wire to generate the heat that toasts your bread)

However superconductors only exist at very low temperatures and even after a hundred years of research the quest for a ‘Room Temperature Superconductor’ has only progressed to a temperature of about 90K (around -180ºC). Very strangely the materials that are now known to become superconducting at the highest temperatures are ceramics that at room temperatures have very high resistances.

At present the best theory we have to explain the phenomenon superconductivity describes it as a pairing up of the electrons in the material, one electron having it’s spin up while its mate’s spin is down. The pair as a whole therefore has no spin and in the strange world of quantum physics they can now zip past the atoms in the material without the collisions that cause resistence.

The image below shows one of the stranger aspects of superconductivity where a magnet is actually being repelled by, and therefore floats above a slab of superconducting material.

Superconductivity – Meissner effect (Credit: MagLab)

Now a group of scientists at the Institute for Theoretical Physics of the University of Heidelberg in Germany has succeeded in opening a new avenue for research by creating a two-dimensional structure of atoms and observing the behavior of the electrons of the atoms. They did this by using focused laser beams to confine the atoms of an ultracold gas into a layer just one atom thick. According to Professor Selim Jochim who heads the research “This means that electrons in the system can only move in two-dimensional planes.”

Then using a technique called radio-frequency spectroscopy, similar to a medical MRI, Professor Jochim’s team discovered that the electrons were pairing up in the same manner as in a superconductor. More than that, they found that they were able to cause the pairings to occur at temperatures several times higher than the known critical temperature of the atoms of the gas. The image below shows a representation of the experimental result.

Superconductivity in a Two Dimensional Structure (Credit: Puneet Murthy)

Whether and how soon this research will lead to large-scale use of superconductors in our electrical grid is unknown. However every new discovery about the phenomenon of superconductivity brings that day a little bit closer.