# Superconductivity by year 12 physics students

Researching Superconductivity by Alfie Mussett

The discovery of superconductivity
Superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes. When he cooled the mercury to the same temperature as liquid helium (which comes out to about -269 degrees Celsius) the mercury’s resistance suddenly disappeared!
He later won a Physics Nobel Prize in 1913 for this discovery.

Born: 21 st September 1853 Groningen, Netherlands                                                Died: 21st February 1926 Leiden, Netherlands

How can the low temperatures for superconductivity be reached?
A branch of Physics called “cryogenics” is employed. Machines are used to pump the heat out of an object to cool it.

Liquefying gases is how lower and lower temperatures are reached and once a gas is liquefied heating it simply causes it to evaporate. So from here it becomes easy to submerge samples in these liquids to see how they respond to very low temperatures, in the case of superconductors, reaching a resistance of zero.

Typical Transition Temperatures
Here is a table of transition temperatures for some metals. The transition temperature is the temperature when a conductor completely loses its resistance. The temperatures are given in kelvin (0K = -273 degrees Celsius).

High-temperature superconductors are exciting because they allow superconductors to be utilised under real-life conditions as opposed to needing the lab conditions to get the temperature cold enough for low-temperature superconductors. This could be used in computing, for example, to produce computer speeds that are several orders of magnitude faster than the best computers are today.

Why are superconductors used in strong magnets?
An example of superconductors being used with strong magnets where ordinary electromagnets just wouldn’t work is in magnetic-levitation. Large objects like trains can be made to “float” on very strong superconducting magnets, eliminating friction entirely and allowing for trains to run at much faster speeds than previously, a test of such technology attaining an incredible speed of 361 miles per hour!

A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. Persistent electric current flows on the surface of the superconductor, acting to exclude the magnetic field of the magnet (Faraday’s law of induction). This current effectively forms an electromagnet that repels the magnet.
A conventional electromagnet would waste much of the electrical energy as heat and need to be much larger to have the same effect and so just wouldn’t be viable to implement.
Superconducting magnets are also used to produce images of inside the human body via a non-intrusive method called MRI scanning.

Superconductivity is maintained in these kinds of mechanisms via application of liquid nitrogen to keep the superconductors at the low temperatures required to maintain superconductivity.

How do superconductors store energy?
A superconductor by its very definition is a substance that has an electrical resistance of absolutely zero. No resistance means the current will not decay over any amount of time provided the substance’s resistance continues to stay at zero.
Since electricity is a form of energy and a superconductor can keep a current indefinitely, they can store electrical energy fairly easily.

How would room temperature superconductors change the world?
Room temperature superconductors would allow for such technology to be employed in everyday household appliances, like computers for instance, and this would result in computer speeds that are simply unthinkable at this point in time. As mentioned earlier, it also allows for trains that travel at incredibly fast speeds, resulting in lower travel times and a much easier time travelling from country to country by train.
Superconductors that function at room temperature would generally allow for a more connected world than ever before.

A small sample of the high-temperature superconductor BSCCO-2223.

http://en.wikipedia.org/wiki/High-temperature_superconductivity

Superconductivity by Manikandan Jeyakanthan

What is superconductivity?

Superconductivity is a phenomenon whereby a conductor has exactly zero electrical resistance and in certain materials there is a complete expulsion of magnetic fields, This occurs when the material is cooled below a characteristic critical temperature. The phenomenon was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon.

Superconductivity is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics.

The History of Superconductors

Superconductors are materials that have no resistance to the flow of electric current and their discovery is one of the last great frontiers of scientific discovery. Not only have the limits of superconductivity not yet been reached, but also the theories that explain superconductor behaviour seem to be constantly under review. In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes of Leiden University.

When he cooled mercury to the temperature of liquid helium, 4 degrees Kelvin (-452F, -269C), its resistance suddenly disappeared. The Kelvin scale represents an “absolute” scale of temperature. Thus, it was necessary for Onnes to come within 4 degrees of the coldest temperature that is theoretically attainable to witness the phenomenon of superconductivity. Later, in 1913, he won a Nobel Prize in physics for his research in this area.

The next great milestone in understanding how matter behaves at extreme cold temperatures occurred in 1933. German researchers Walther Meissner (below left) and Robert Ochsenfeld (below centre) discovered that a superconducting material would repel a magnetic field (below right).

A magnet moving by a conductor induces currents in the conductor. This is the principle on which the electric generator operates. But, in a superconductor the induced currents exactly mirror the field that would have otherwise penetrated the superconducting material – causing the magnet to be repulsed. This phenomenon is known as strong diamagnetism and is today often referred to as the “Meissner effect” (an eponym). The Meissner effect is so strong that a magnet can actually be levitated over a superconductive material.

Use of Superconductors

Magnetic levitation is an application where superconductors perform extremely well. Transport vehicles such as trains can be made to “float” on strong superconducting magnets, virtually eliminating friction between the train and its tracks. Not only would conventional electromagnets waste much of the electrical energy as heat, they would have to be physically much larger than superconducting magnets. A landmark for the commercial use of MAGLEV technology occurred in 1990 when it gained the status of a nationally funded project in Japan. The Minister of Transport authorized construction of the Yamanashi Maglev Test Line, which opened on April 3, 1997. In December 2003, the MLX01 test vehicle attained an incredible speed of 361 mph (581 kph).

Although the technology has now been proven, the wider use of MAGLEV vehicles has been constrained by political and environmental concerns (strong magnetic fields can create a bio-hazard). The world’s first MAGLEV train to be adopted into commercial service, a shuttle in Birmingham, England, shut down in 1997 after operating for 11 years. A Sino-German maglev is currently operating over a 30-km course at Pudong International Airport in Shanghai, China. The U.S. plans to put its first (non-superconducting) Maglev train into operation on a Virginia college campus.

JR-Maglev at Yamanashi, Japan test track in November 2005

Theories of superconductivity

Since the discovery of superconductivity, great efforts have been devoted to finding out how and why it works. During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of “conventional” superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957). Generalizations of these theories form the basis for understanding the closely related phenomenon of superfluidity, because they fall into the Lambda transition universality class. However, the extent to which similar generalizations can be applied to unconventional superconductors is still controversial. The four-dimensional extension of the Ginzburg-Landau theory, the Coleman-Weinberg model, is important in quantum field theory and cosmology. Superfluidity of helium and superconductivity both are macroscopic quantum phenomena.

Superconducting phase transition

In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature Tc. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from around 20 K to less than 1 K. Solid mercury, for example, has a critical temperature of 4.2 K.

Behaviour of heat capacity (cv, blue) and resistivity (ρ, green) at the superconducting phase transition.

Sources of information:

1) The Internet for finding about “superconductivity

2) Book to find out about “Use of Superconductors”

SOURCE – “High TC superconductivity”, writer – Leslie Brunetta, written in 2010.

3) Magazine – FreeScience 2011 edition, page 65 to find out about mechanical properties and the history of Superconductors.

Superconductivity by Wing Chung Hau

Superconductivity is when a certain material conducts an electric current with zero resistance. Only certain materials have demonstrated this property and only at extremely low temperatures.

A superconductor is a material that demonstrates superconductivity, it is a perfect conductor. A closed loop of superconducting wire carrying a current will continue to carry the current as long as it is kept below the critical temperature Tc below which it becomes a superconductor, this current is called a persistent current.

How it works

As the conductor is cooled, the resistance drops. For normal conductors, the resistance will continue to fall but will never become zero, however for superconductors, once the temperature reaches a certain point, all resistance disappears.

Table showing some superconducting materials and their critical temperatures.

 Materials Tc/K Zinc 0.87 Mercury 4.15 Lead 7.19 Niobium 9.26

History of Superconductivity

Superconductivity was discovered on April 8, 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently-produced liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared.

In 1987, J. Georg Bednorz and K. Alex Muller from IBM’s Research Laboratory in Zurich received a Nobel Prize for their discovery of new ceramic superconductors with exceptionally high transition temperatures.

http://www.nobelprize.org/nobel_prizes/physics/laureates/1987/

Social effects of Superconductivity

Superconductors have a wide range of uses such as MRI scanning, mass spectrometry, magnetic levitation devices and super computers.

Promising future applications include high-performance smart grid, electric power transmission, transformers, power storage devices, electric motors, magnetic levitation devices, fault current limiters, nanoscopic materials, composite materials and superconducting magnetic refrigeration.

MagLev train is a train that “floats” on strong superconducting magnets, virtually eliminating friction between the train and its tracks, this allows them to reach very high speeds which would lead to commuters being able to travel very quickly.

Benefits and Risks

The benefits of superconductors are that there is no resistance; this means that they can be used for effective storage and transfer of electricity; they are also used for MRI scans which are very important in hospitals and medical studies. They also allow the use for MagLev trains which allows people to get from one place to another very quickly, reducing time spent on travelling.

The problems with superconductors are that currently, they have to operate at extremely low temperatures which can be costly; they also emit strong magnetic fields which can affect humans in different ways such as brain cancer.

Superconductivity by Aslam Sookia

What is superconductivity?

Superconductivity is where certain materials achieve zero electrical resistance and emit a magnetic field when cooled below a certain temperature (its critical temperature Tc.)

In 1911, H. Kammerlingh Onnes was experimenting with mercury using liquid helium; the refrigerant of the time, and had discovered that below 4.1K it had no electrical resistance. His discovery had been demonstrated by a current running through a lead ring with no measurable reduction of current. Because there is no resistance, a superconducting wire ring could supposedly have a current running through it for billions of years.

Meissner effect

In 1933, German Physicists Walther Meissner and Robert Ochsenfeld had discovered that when a material becomes a super conductor, it emits a magnetic field from its interior because of its zero resistance. When exposed to a weak magnetic field, the material is able to repel almost the entire field back down towards the magnet, which makes the superconductor levitate.

The graph below shows how resistance is affected by temperature for superconductive and non-superconductive metals.

For the superconductor, the resistance drop straight to zero at a certain temperature (its critical temperature)

Applications of superconductivity

Sensitive magnometers

Fast digital circuits

Superconducting electromagnets (used in maglev trains)

Particle detectors

Electric motors and generators

Sensing element of the SQUID

Benefits
• Because the resistance of superconductive material is so low, there is no current wastage when they are used to conduct electricity.
• When used in the process of magnetic levitation, no kinetic energy is wasted due to friction from contact with the ground.

Problems
• To show their properties, and be of any use, they must be at critical temperature, which can be costly.
• They emit strong magnetic fields which can affect humans by causing blindness, sterility, brain cancer and other things.

Bibliography

http://en.wikipedia.org/wiki/Superconductivity

http://hyperphysics.phy-astr.gsu.edu/%E2%80%8Chbase/solids/scond.html

http://science.howstuffworks.com/environmental/energy/superconductivity.htm

http://hyperphysics.phy-astr.gsu.edu/%E2%80%8Chbase/solids/meis.html

Superconductivity by Matthew Kelly

Superconductivity is exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature.

Conditions for Superconductivity

The material must be cooled below a characteristic temperature, known as its superconducting transition or critical temperature (Tc).

The current passing through a given cross-section of the material must be below a characteristic level known as the critical current density (Jc).

The magnetic field to which the material is exposed must be below a characteristic value known as the critical magnetic field (Hc).

These conditions are interdependent, and define the environmental operating conditions for the superconductor.

Here is a table showing the Critical temperature for various materials.

 Material Tc/K Niobium-germanium 0.23 Zinc 0.87 Mercury 4.15 Lead 7.19 Niobium 9.26 Yttrirum-barrium copper oxide 93 Thallium-calcium-bismuth copper oxide 125

History of superconductivity

Superconductivity was discovered on April 8, 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently-produced liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared.

Benefits and Risks.

Obvious benefits include: Zero electrical DC resistance-

Superconductors are also able to maintain a current with no applied voltage, superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years.

Risks:

To show their properties, and be of any use, they must be at critical temperature, which can be costly. Very low temperatures restricted range for operating temperature. Since the world record for the highest critical temperature stands at 138 K, there is still a long way to go before superconductors are available to the average user at room temperature. It is impractical for handheld, consumer devices to have liquid nitrogen running through them.

They emit strong magnetic fields which can affect humans by causing blindness, sterility, brain cancer and other things.

Superconductors by Pameer Saeed

This report will describe what is a superconductor and as well as different types of superconductors and uses of superconductor.

History of superconductor

In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes of Leiden University. When he cooled it to the temperature of liquid helium, 4 degrees Kelvin (-452F, -269C), its resistance suddenly disappeared. The Kelvin scale represents an “absolute” scale of temperature. Thus, it was necessary for Onnes to come within 4 degrees of the coldest temperature that is theoretically attainable to witness the phenomenon of superconductivity. Later, in 1913, he won a Nobel Prize in physics for his research in this area.

What is a superconductor?

A superconductor is a material that can conduct electricity (or transport electrons from one atom to another with no resistance.)This means no heat, sound or any other form of energy would be released from the material when it has reached “critical temperature” (Tc), or the temperature at which the material becomes superconductive.

Unfortunately, most materials must be in an extremely low energy state (very cold) in order to become superconductive. Research is underway to develop compounds that become superconductive at higher temperatures. Currently, an excessive amount of energy must be used in the cooling process making superconductors inefficient and uneconomical.

Types of superconductor

There are two types of superconductors:

The Type 1 category of superconductors is mainly comprised of metals and metalloids that show some conductivity at room temperature. They require incredible cold to slow down molecular vibrations sufficiently to facilitate unimpeded electron flow in accordance with what is known as BCS theory. BCS theory suggests that electrons team up in “Cooper pairs” in order to help each other overcome molecular obstacles – much like race cars on a track drafting each other in order to go faster.

Some example of type 1 superconductors

Lanthanum (La)
Tantalum (Ta)
Mercury (Hg)

Except for the elements vanadium, technetium and niobium, the Type 2 category of superconductors is comprised of metallic compounds and alloys. They achieve higher Tc’s than Type 1 superconductors by a mechanism that is still not completely understood.

Some example of type 2 superconductors

SrTiO3
UGe2
URhGe2 AuIn3

Above (magnetic field against Temperature) graphs shows that type 1 superconductors produce less magnetic field in their critical temperature compare to type 2. Type 2 superconductor produce very large magnetic field in their critical temperature and they can be used to hold large weight.

Uses of superconductors

Magnetic-levitation is an application where superconductors perform extremely well. Transport vehicles such as trains can be made to float on strong superconducting magnets, virtually eliminating friction between the train and its tracks.

Another area where superconductors can perform a life-saving function is in the field of bio-magnetism. Doctors need a non-invasive means of determining what’s going on inside the human body. By impinging a strong superconductor-derived magnetic field into the body, hydrogen atoms that exist in the body’s water and fat molecules are forced to accept energy from the magnetic field. They then release this energy at a frequency that can be detected and displayed graphically by a computer.

Recently, power utilities have also begun to use superconductor-based transformers and fault limiters. The Swiss-Swedish company ABB was the first to connect a superconducting transformer to a utility power network in March of 1997. ABB also recently announced the development of a 6.4MVA (mega-volt-ampere) fault current limiter – the most powerful in the world. This new generation of HTS superconducting fault limiters is being called upon due to their ability to respond in just thousandths of a second to limit tens of thousands of amperes of current. Advanced Ceramics Limited is another of several companies that makes BSCCO type fault limiters. Inter-magnetics General recently completed tests on its largest (15kv class) power-utility-size fault limiter at a Southern California Edison (SCE) substation near Norwalk, California. And, both the US and Japan have plans to replace underground copper power cables with superconducting BSCCO cable-in-conduit cooled with liquid nitrogen. By doing this, more current can be routed through existing cable tunnels. In one instance 250 pounds of superconducting wire replaced 18,000 pounds of vintage copper wire, making it over 7000% more space-efficient.

Sources:-

Internet:

http://www.superconductors.org/INdex.htm

(14/03/2013)

http://rmp.aps.org/abstract/RMP/v82/i1/p109_1

(16/03/2013)

Magazine:

R&D magazine

Release date: Mon, 02/25/2013

Article By: David L. Chandler

Book:

1) Introduction to Superconductivity (Dover Books on Physics)

By Michael Tinkham

Publication Date: Jun. 14th, 2004

2) Superconductivity (second edition)

By Charles P. Poole Jr., Horacio A. Farach, Richard J. Creswick, Ruslan Prozorov

Publication Date: 2007

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