Meissner Effect is the effect that converts a material from a normal state to a superconducting state. When a material is called below a specified temperature at which the magnetic field from the interior of the material is exploded, then this material is transformed into the superconductor. This phenomenon is called the Meissner Effect.

The temperature required to convert the material into the superconductor is called the transition temperature. This transition temperature is near absolute temperature (0 kelvin). This superconductor material has zero electric resistance. The main importance of the Meissner Effect is magnetic levitation, which is a process by which a body is suspended with no support except a magnetic field.

Superconducting State

The superconducting state is the state where the material has zero electric resistance. At this stage, the material loses all the resistance of the flow of electric current. When the material is cooled below the transition temperature, it converts into the superconductor and reaches the superconducting state. Mercury reaches the superconducting state when cooled down below 4.1 kelvin.

What is the Meissner Effect?

Walther Meissner and Robert Ochsenfeld, two German physicists, obtained the physical process of the Meissner effect in the year 1933. Meissner Effect is the expulsion of the magnetic field, which converts a material from a normal state to a superconducting state when cooled down below the transition temperature.

When a magnetic field is applied at the higher value of temperature to the transition temperature, the superconductor has a minor effect. These magnetic fields passed through the superconductor quickly. At the lower value of temperature to the transition temperature, the magnetic field is thrown out from inside the superconductor and bends on all sides of it when the magnetic field is applied. 

This explosion of the magnetic field is the generation of magnetisation inside the superconductor due to no resistance flow of surface currents. This generated magnetization inverse and opposite to the applied magnetic field, which neuters the magnetic field around the superconductor.

Meissner State

The state at which the material becomes a superconductor is called the Meissner state. When the magnetic field increases further to the specified value, and the material behaves like the ordinary conductor, the Meissner state is broken down. This specified magnetic field value is known as the critical magnetic field. 

The more the value of temperature below the transition temperature decreases, the more the value of the critical magnetic field is increased. The Meissner state can only be broken down when the magnitude of the electric field is too strong. On the basis of this breakdown, there can be two types of superconductors that may form.

• Type-I Superconductor: This superconductor excludes the magnetic field until the superconductivity is destructed abruptly. Later, the magnetic field penetrates completely—the critical value of the type-I superconductor too low.

• Type-II Superconductor: The type two superconductors keeps out the entire magnetic field until a lower critical value is reached. The magnetic flux quantum, which penetrates the superconductor, is now appearing. In this zone, the metal is no longer remain a superconductor. If the value of the field increases to a higher critical value, then the metal stops being a superconductor. This type of superconductor is made with material that has high electric resistivity.

Diamagnetism property for Superconductor

The Meissner Effect says that the ideal diamagnetism is the important property of the superconducting state. This statement can be proved with the relation of magnetic field and magnetic field intensity.

The Meissner Effect suggests that the value of the magnetic field inside a superconductor is zero. 

 B=0 

The magnetic induction inside the specimen for the normal conditions is given by the following equation.

B=o (H+I)

Here, I is the magnetization which is generated inside the specimen and H is the magnetic field applied externally.

By both equation, we have,

0=o (H+I)

H=-I

H /I =-1=X

The diamagnetic material susceptibility is equal to -1, so the material is ideally diamagnetic.

Diamagnetism of superconductor

The superconductor has the magnetic susceptibility of -1 which makes it perfect diamagnetism. This diamagnetic keeps magnetization which resists any applied magnetic field, thus the superconductor feels repulsion by any magnetic field. 

This repulsion force is the main reason for the levitation of a superconductor, under the application of a magnet. If this magnetic field is separate or the temperature of the superconductor rises above the transition temperature, the magnetization and surface currents disappear, and the levitation will stop.

Contradiction of Meissner Effect

The Maxwell’s equation for electrodynamics is given by,

E=-dB/dt

The electric field is equal to zero for a superconductor. 

0=-dB/dt

0=dB/dt

B=constant

According to Meissner, the magnetic field inside a superconductor is zero, but in this case the magnetic field has constant value and is not equal to zero.

Meissner Effect Importance

The Meissner effect has importance in the field of superconductivity of the superconductor. The magnetic levitation, which is the main concept of a bullet train and hyperloop, is also discovered with the help of the Meissner effect. The importance of the Meissner Effect is listed below.

• The Meissner Effect helps to understand the theory of superconductivity. 
• The Meissner Effect is used in magnetic levitation, which means a body is suspended with no support except a magnetic field.
• In coils of superconducting magnets, the Meissner Effect is applicable.
• The Meissner Effect says that the ideal diamagnetism is the crucial property of the superconducting state.
• The Meissner Effect keeps the importance in high speed or fifth means of transmission such as bullet trains and hyperloops.

Conclusion

Meissner Effect talks about the expulsion of the magnetic field, which helps convert material from normal state to superconducting state, which is when cooled below the critical temperature or transition temperature. The major importance of the Meissner Effect is in the field of superconductivity and magnetic levitation.