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If you've ever used a computer or laptop, you may have noticed that the power supply or battery gets warm after a while. This warmth is actually thermal energy that comes from electrical energy. But this heat is unwanted because it's not being used for anything useful. Instead, it's just being lost to the air. But what if we could have no energy loss? That would mean everything would be more efficient! Is this even possible? That's where superconductivity comes in!

What are superconductors?

All materials that conduct electricity have some resistance, even the best ones. When electricity flows through a material, it heats up, which increases its resistance. But regular conductors can have their resistance lowered if they get colder.

Superconductors, on the other hand, have a special property called the critical temperature. When a superconductor's temperature goes below this critical point, its resistance suddenly drops down to zero. This means that superconductors are able to conduct electricity with zero resistance, which is pretty amazing!

The resistance of Mercury

One of the most common examples of a superconductor is Mercury at the critical temperature of 4.2 Kelvin (-269.2°C). This was discovered by the Dutch physicist Heike Kamerlingh Onnes in 1911.

The resistance of Mercury relative to the temperature in Kelvin
The resistance of Mercury relative to the temperature in Kelvin

When Onnes was studying the resistance of different metals with liquid helium, he made a fascinating discovery. As he cooled a of Mercury, he noticed that its resistance suddenly dropped to zero when the temperature went below 4.2 Kelvin. This temperature is now known as the critical temperature (Tc) and the amazing phenomenon is called superconductivity.

If we try to measure the resistance of a superconductor using a three-digit ohmmeter, it will read 0.00Ω. But this doesn't mean that the resistance is actually zero – it's just lower than 0.01Ω, which the ohmmeter can't detect. There are other ways to measure such low resistances, but using an ohmmeter isn't one of them when working with superconductors. This also means that evenconductors can't have an absolute zero resistance (though it's theoretically accepted as zero).

Conditions for superconductivity

It's true that superconductors have very high efficiency due to their near-zero resistance, but they aren't used in everything for conducting electricity because the conditions for superconductivity are difficult to achieve. Common conductors like copper, gold, and silver don't exhibit superconductivity.

There are three conditions that must be met for a material to become a superconductor:

  1. Critical temperature (Tc): The temperature of the conductor must be below a certain critical temperature (Tc).
  2. Critical current density (Jc): The current flowing through a specific cross-section of the conductor should be below a certain critical current density (Jc).
  3. Critical magnetic field strength (Hc): The magnetic field strength to which the conductor is exposed must be below a certain critical magnetic field strength (Hc).

These values are unique to each superconductor and must be carefully controlled and maintained for the material to exhibit superconductivity. This is why superconductors are currently limited to very specific applications where these conditions can be met, such as in MRI machines and particle accelerators.

Critical temperature

Let’s focus on the more important and commonly known condition, critical temperature.

Three conditions affecting superconductivity


Scientists have been searching for a superconductor with a higher critical temperature for a long time. In 1911, Mercury was found to have a critical temperature of 4.2K (-269.2°C). Currently, the superconductor with the highest critical temperature is Mercury Barium Thallium Copper Oxide, with a critical temperature of 139 Kelvin (-134.15°C).

While this is a significant improvement over Mercury, it's still extremely cold compared to room temperatures. This is why superconductors aren't widely used, as the cooling requirements make them costly and impractical for most applications.

Here's a table showing the critical temperatures and critical magnetic fields for different materials: In addition to zero resistance, superconductivity also exhibits other fascinating phenomena, such as the Meissner effect, which is the exclusion of magnetic fields.

The Meissner effect

The magnetic field is excluded from the superconductor, causing it to levitate and providing a perfect magnetic shield. This effect is used in high-speed trains, which use superconducting magnets to levitate above the tracks and eliminate the force of friction, allowing them to reach speeds of up to 603 kilometers per hour.

The use of superconductors in transportation has many potential benefits. In addition to the elimination of friction, which can greatly increase speed and efficiency, superconducting motors and generators can be more compact and lighter than traditional ones. This can lead to significant savings in energy, weight, and space, making it an attractive option for various modes of transportation.

However, the high cost of cooling systems required to maintain superconductivity at low temperatures is still a major challenge that needs to be overcome before superconductors can be widely used in transportation or other applications. Nevertheless, ongoing research is focused on developing room-temperature superconductors, which could revolutionize various industries in the future.

What are the applications of superconductors?

Yes, superconductors are essential for devices that require low resistance and a high magnetic field. Some of the most common applications of superconductors include MRI scanners, generators, high-speed trains, and particle accelerators.

Another important application of superconductors is the superconducting quantum interference device (SQUID). SQUIDs are highly sensitive magnetometers that are used to measure extremely small magnetic fields. The device relies on superconducting loops containing two Josephson junctions, as shown in the image below.

When a tiny magnetic field is present around the SQUID, it causes an interference effect that depends on the strength of the magnetic field. This effect can be measured and used to detect and measure extremely small magnetic fields.

Josephson junctions are devices that have a supercurrent continuously flowing through them. Supercurrent is the current that flows through superconducting materials without any dissipation. These junctions are essential for the operation of SQUIDs and other superconducting devices.

A diagram of SQUID
A diagram of SQUID

Superconductivity - key takeaways Superconductors offer zero resistance to the flow of current. There is no energy loss as a result. When the temperature of a conductor that exhibits superconductor properties falls below the critical temperature (Tc), it shifts into a superconductive state. There are three conditions that affect superconductivity: critical temperature (Tc), critical current density (Jc), and critical magnetic field strength (Hc). Superconductors are used in various applications, such as MRI scanners, high-speed trains, and particle accelerators.


What is a superconducting magnet?

A superconducting magnet is an electromagnet that is made from superconducting coils. These superconducting coils show zero resistance to the current flow, allowing a supercurrent to flow through itself, which creates an intense magnetic field.

What is meant by superconductivity?

Superconductivity is the phenomenon that explains the ability of specific conductors to show zero resistance to the current flow under a certain temperature called the critical temperature (Tc).

How does superconducting levitation work?

Superconducting levitation works depending on the Meissner effect, which explains the exclusion of magnetic fields. This exclusion causes the permanent magnet to levitate in a static way.

What causes superconductivity?

Superconductivity is the phenomenon that explains the ability of specific conductors to show zero resistance to the current flow under a certain temperature called the critical temperature (Tc).

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