Superconductivity

Some things move power very well.

These things must be very cold. When they get cold, power flows with no stop. This is called superconductivity.

In these cold things, power moves easily. It can even flow in a loop forever.

This happens because the power does not get stuck.

These materials also push magnets away. This makes the material float in the air. It looks like magic!

Scientists use these for big machines. They help make tools for doctors. They also help make big tools for science.

It is amazing how cold things work.

Some materials can move electricity with no loss. We call this superconductivity.

A scientist named Heike Kamerlingh Onnes found this in 1911. He was studying mercury. He made it very cold. At 4.2 K, the resistance vanished. Resistance is what slows down electricity.

Superconductors also do something special with magnets. They push magnetic fields out of their insides. This is called the Meissner effect. Because of this, a superconductor can float above a magnet.

Most superconductors need to be extremely cold. This is hard to do. In 1986, scientists found new materials. These are called high-temperature superconductors. They work even when using liquid nitrogen to stay cold. Liquid nitrogen is much cheaper than other coolants. Today, we use these materials in many places. They help make MRI machines for doctors. They also help run big particle accelerators.

These machines use super magnets to study science.

Superconductivity is a special way that some materials act when they get very cold. In a normal wire, electricity faces resistance, which is a force that slows it down. This resistance can even turn energy into heat. But in a superconductor, this resistance vanishes completely. This means electricity can flow through a loop of wire forever without any power source.

These materials also have a unique relationship with magnets. They push magnetic fields out of their insides. This is called the Meissner effect. Because they push the magnetic field away, a superconductor can actually float above a magnet.

How does this happen? It works because of a specific change that occurs at a critical temperature. As a material cools, its resistance usually drops slowly. However, a superconductor reaches a point where the resistance drops abruptly to zero.

This change is a quantum mechanics phenomenon. In 1935, brothers Fritz and Heinz London showed that the Meissner effect happens to keep energy at its lowest level. Later, in 1957, scientists Bardeen, Cooper, and Schrieffer explained the microscopic way it works. They found that electrons form special pairs called Cooper pairs. These pairs move through the material together without being slowed down by anything.

Humans first discovered this amazing thing in 1911. A Dutch physicist named Heike Kamerlingh Onnes found it while studying solid mercury. He used liquid helium to make the mercury extremely cold. At 4.2 K, he saw the resistance suddenly disappear.

It took a long time to find the exact details of his discovery. Scientists only reconstructed the precise date and story a century later by finding his old notebooks. Other materials were found to work later, like lead in 1913 and niobium nitride in 1941.

Finding materials that work at higher temperatures was a huge goal. In 1986, scientists found ceramic materials that could superconduct at higher temperatures. A scientist named Ching-Wu Chu found that changing the material to YBCO made it even better. This was important because it allowed the use of liquid nitrogen as a coolant. Liquid nitrogen is much cheaper than liquid helium and boils at 77 K.

Today, many different types of materials are studied, including thin layers of graphene. These 2D materials can sometimes be tuned to act as superconductors.

We use superconductivity in many parts of our modern world. One of the most common uses is in MRI machines used by doctors. These machines use super magnets to take pictures of the inside of the body.

Superconductors are also used in huge particle accelerators to study science. Some special wires, like niobium-titanium, are used because they are easy to make into shapes. These materials act like the workhorses of the scientific world. From medical tools to giant machines, superconductivity helps us see and do much more.

Superconductivity is a unique state of matter characterized by specific physical properties. In this state, a material's electrical resistance vanishes entirely. This means an electric current can flow through a superconducting loop indefinitely without a power source.

Superconductors also exhibit the Meissner effect. This is the complete expulsion of magnetic fields from the material's interior. This phenomenon occurs as the material transitions into its superconducting state. Because of these properties, superconductors can interact with magnets in remarkable ways, such as levitation.

The transition to superconductivity happens at a specific critical temperature. In ordinary metallic conductors, resistance decreases gradually as the temperature drops. However, a superconductor experiences an abrupt drop to zero resistance once it hits its critical temperature.

The Meissner effect is a key part of this mechanism. It shows that superconductivity is not just perfect conductivity. It is a distinct quantum mechanical phenomenon. In 1935, physicists Fritz and Heinz London developed equations to explain this. They showed that the Meissner effect results from minimizing electromagnetic free energy.

Scientists have identified different categories of superconductors. In 1950, physicists Ginzburg and Landau developed a theory to explain macroscopic properties. This theory helped Abrikosov categorize superconductors into Type I and Type II. In the 1950s, the BCS theory provided a microscopic explanation. Proposed by Bardeen, Cooper, and Schrieffer in 1957, it describes how electrons form Cooper pairs. These pairs interact through the exchange of phonons, which are vibrations in the material. This movement creates a superfluid of electrons that flows without resistance.

The history of this field began with Heike Kamerlingh Onnes. On April 8, 1911, he discovered superconductivity while studying solid mercury. He used liquid helium as a refrigerant to reach extremely low temperatures. At 4.2 K, he observed the resistance suddenly disappear.

Other materials were discovered later, such as lead in 1913 and niobium nitride in 1941. A major breakthrough occurred in 1986 with the discovery of cuprate-perovskite ceramics. These materials could superconduct at much higher temperatures. Ching-Wu Chu later found that creating YBCO raised the temperature further. This allowed scientists to use liquid nitrogen, which boils at 77 K, as a coolant.

Superconductivity has massive economic and scientific significance. In 2014, a European consortium estimated global economic activity related to superconductivity at five billion euros. About 80% of this total comes from MRI medical imaging systems. Superconductors are also vital for high-energy-particle accelerators.

For these machines, researchers use specialized alloys. Niobium-tin is a compound of three parts niobium and one part tin. It can support massive current densities and magnetic fields up to 20 tesla. However, it is brittle and difficult to make. Niobium-titanium is more ductile and easier to fabricate. It has become the "workhorse" material for many supermagnets.

Modern research is now exploring 2D materials like graphene. Scientists can twist layers of graphene to create a "moiré" pattern. This pattern creates hexagonal cells that act like atoms. By adding electrons to these systems, researchers can induce superconductivity. In 2018, a twisted bilayer graphene sheet showed superconductivity at 1.7 K. Other researchers have observed "chiral superconductivity" in rhombohedral graphene. These 2D systems are highly tunable. They allow scientists to test many different configurations quickly. This work is very important for the future of quantum computing.

Superconductivity connects many different areas of physics. It links the study of electricity to quantum mechanics and thermodynamics. The Josephson effect, predicted in 1962, allows current to flow between superconductors separated by an insulator. This effect is used in SQUIDs to make incredibly precise measurements. It even helps scientists measure the Planck constant. From the tiny scale of electron pairs to the massive scale of particle accelerators, superconductivity remains a central mystery of the physical world.