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# Superconductivity

Superconductivity is a special property of certain materials called superconductors. These materials exhibit remarkable behavior when they are cooled to very low temperatures and are discussed in the next section.

The discovery of superconductivity in 1911 by Dutch physicist Heike Kamerlingh Onnes was a groundbreaking development in condensed matter physics.

## Characteristics of Superconductors

1. Critical Temperature (TC)

Each superconductor has a specific temperature below which it becomes superconductive. This temperature is called the critical temperature. Above this temperature, the material behaves like a normal conductor with electrical resistance.

2. Zero Electrical Resistance

When a superconductor is cooled below its critical temperature, it has no electrical resistance. This allows electric current to flow through it without any energy loss. The current can continue to flow indefinitely without weakening as long as the temperature remains below the critical value.

3. Perfect Diamagnetism

Superconductors completely expel magnetic fields from their interior. It means that the magnetic field inside a superconducting material is zero when it is in its superconducting state. This property is known as the Meissner effect.

4. Critical Magnetic Field (HC)

Superconductors can expel magnetic fields up to a certain strength. The maximum strength of the magnetic field that a superconductor can repel while maintaining its superconducting properties is known as the critical magnetic field. If the magnetic field exceeds this critical value, the superconductor will lose its zero resistance and perfect diamagnetism and revert to a normal state.

Based on their properties, superconductors are classified into Type I and Type II superconductor. Examples of Type I superconductors include mercury, aluminum, and lead. Examples of Type II superconductors are niobium and niobium-titanium alloys.

## Theories of Superconductivity

There are two main theories of superconductivity:

1. BCS Theory (Bardeen-Cooper-Schrieffer Theory): Proposed in 1957 by John Bardeen, Leon Cooper, and Robert Schrieffer, the BCS theory describes superconductivity as a result of electron pairing due to interactions with lattice vibrations (phonons) in the material. According to BCS theory, electrons form pairs known as Cooper pairs at low temperatures, which collectively condense into a quantum state with zero electrical resistance.

2. Ginzburg-Landau Theory: Developed independently by Vitaly Ginzburg and Lev Landau in 1950, this theory provides a phenomenological description of superconductivity based on the macroscopic wave function, known as the order parameter. The Ginzburg-Landau theory describes the behavior of superconductors near the critical temperature and predicts the existence of a second-order phase transition.

## Applications of Superconductivity

Superconductors are important because they have many practical applications, including:

1. Magnetic Resonance Imaging (MRI): Superconducting magnets, capable of generating extremely powerful and stable magnetic fields, are the backbone of MRI technology. They allow doctors to capture detailed images of the human body without ionizing radiation.
2. Magnetic Levitation (Maglev) Trains: High-speed maglev trains utilize superconducting magnets to levitate the train cars above the track, enabling frictionless, energy-efficient transportation at speeds exceeding 600 km/h. This technology is already in use in several countries, showcasing the practical benefits of superconductivity.
3. Particle Accelerators: Superconducting magnets guide and focus particle beams over long distances in particle accelerators like the Large Hadron Collider (LHC).
4. Superconducting Quantum Computing: Superconductors also play a crucial role in developing quantum computers. The ability of superconducting materials to carry electricity without resistance makes them ideal for the delicate quantum circuits required in these next-generation computing devices, which promise to revolutionize fields like cryptography, materials science, and drug discovery.

Article was last reviewed on Thursday, July 18, 2024