×

Magnetic and Electromagnetic Properties of Superconductors

Top
Download PDF
FAQ

Superconductors

Bookmark added to your notes.
View Notes
×

Superconductivity was first found in 1911 when mercury was cooled to roughly 4 degrees Kelvin by Dutch physicist Heike Kamerlingh Onnes, which acquired him the 1913 Nobel Prize in material science. It is a material that is capable of superconducting at low temperatures.

A superconductor example is “Tungsten”, other examples are “Tin,”, “Zinc,” these materials are when cooled at a critical temperature, they suddenly become superconductors. 

One of the known applications of a superconductor is, they are used in generating the mighty magnetic field between 20 - 30 T.

On this page, you will get sufficient information on superconductors, like the properties of superconductors and applications of superconductors.


Superconductor Materials

A superconductor is a component or metallic alloy which, when cooled under a specific limit temperature, the material significantly loses all electrical obstruction. 

On a fundamental level, superconductors can permit electrical flow to stream with no energy loss (albeit, by and by, an ideal superconductor is difficult to produce). This kind of current is known as a supercurrent. 

The critical/edge temperature beneath which a material changes into a superconductor state is assigned as Tc, which represents basic (critical) temperature. Not all materials transform into superconductors, and the materials that do, have their own value or estimation of Tc.


Examples of Superconducting Materials

The resistivity of most metals increments with expansion in temperature and the other way around. There are a few metals and chemical compounds whose resistivity becomes zero when their temperature is brought close to 0 Kelvin or - 273°C. At this stage, such metals or compounds are said to have achieved superconductivity.

For instance, Mercury becomes superconducting at around 4.5 Kelvin (- 268.5°C). The progress from typical conductivity to superconductivity happens unexpectedly; it happens over an exceptionally restricted range of temperature, i.e., about 0.05 K.

So, the temperature at which the progress happens from the condition of ordinary conductivity (such as Mercury, as mentioned above) to that of superconductivity is called transition/changing temperature.


Types of Superconductors

Superconductors are categorized into types: type 1 and type 2 superconductors.

Type 1 Superconductors

Type I superconductors are delicate superconductors. They are generally pure examples of certain components for example metals. They have almost no utilization in technical applications.

These types of superconductors act as conductors at room temperature, yet when cooled beneath Tc, the sub-atomic movement inside the material decreases sufficiently that the progression of current can move unobstructed.

Type 2 Superconductors

Type 2 superconductors are hard superconductors. They are typically combinations of metals with a high value of resistivity in ordinary states. These are valuable when contrasted with Type 1 materials. 

Type 2 superconductors are not especially acceptable conductors at room temperature, the progress to a superconductor state is more continuous than Type 1 superconductors. The system and the actual reason for this adjustment in the state aren’t, as of now, completely comprehended. Type 2 superconductors are ordinarily metallic alloys and compounds.

Examples of superconducting materials of type 2 are niobium and vanadium. 


[Image will be uploaded soon]               


Magnetic and Electromagnetic Properties of Superconductors

The properties of superconductors lie hereunder:

1. Critical Field 

Use of an adequately strong magnetic field to superconductors causes the obliteration/destruction of their superconductivity, i.e., the rebuilding of their normal conducting state. 

The critical value of the magnetic field for the obliteration of superconductivity is meant by Hc and is practically identified with temperature as;

Hc = Hc (0) [1 - T2/Tc2]

Where

 Hc(o) = critical field at 0 K, and has a particular value for every material.

Point to Note:

The lower the temperature, the higher the estimation of  Hc and the most increased critical temperature happens when there is no magnetic field. 

In this manner, we track down that the superconducting state is steady just in some definite ranges of magnetic fields and temperatures. For higher fields and temperatures, the ordinary state is more steady.

2. The Meissner Effect

As we stated above, a type 1 superconductor as a long, thin cylinder or ellipsoid remaining parts superconducting at a fixed temperature as an axially arranged magnetic field is applied, given the applied field doesn't surpass a critical value ( Hc). 

Under these conditions, superconductors prohibit the magnetic field from their inside, as could be anticipated from the laws of electromagnetism and the way that the superconductor has no electric obstruction.

An amazing impact happens if the magnetic field is applied similarly to a similar sort of sample at a temperature over the transition temperature and is then held at a fixed value while the sample is cooled. It is tracked down that the example removes the magnetic flux, as it becomes superconducting. We call this effect the Meissner Effect.

3. High-Frequency Electromagnetic Properties

The energy gap in a superconductor directly affects the absorption of electromagnetic radiation. The photon's energy (E) is identified with its recurrence/frequency () by Planck’s relationship, E = hν.

Here,

"h" is Planck's steady (6.63 × 10−34 Joule-second). In the absorption process, a photon (a quantum of electromagnetic energy) is consumed, and a Cooper pair is broken; the two electrons in the pair become energized. At low temperatures, at which an immaterial part of the electrons are thermally excited to states over the gap, the superconductor can absorb energy just in a quantized sum that is, at any rate, double the gap energy (at total zero, 2Δ0). 

Henceforth the superconductor can retain electromagnetic energy just for frequencies in any event as extensive as 2Δ0/h.

FAQ (Frequently Asked Questions)

1. Describe Silbee’s rule.

Ans:  At the point when a current through the superconductor is expanded past critical value Ic(T), the superconductor again turns into a normal conductor. The magnetic field which causes a superconductor to get typical from a superconducting state isn't really an external magnetic field, it might emerge because of the electric flow stream in the conductor. 


The superconductivity may arise when the current surpasses the critical value which at the outside of the wire will create a critical field Hc


However, the superconductivity may get destroyed when the current exceeds the critical value which at the surface of the wire produces a critical field  Hc, given by;


            Ic = 2πHc ; this is known as Silsbee's rule.

2. Explain Magnetic-Flux Quantization.

Ans: The laws of quantum mechanics direct that electrons have wave properties and that the properties of an electron can be summarized in what is known as a wave function. 


If a few wave functions are in stage (i.e., act as one), they are supposed to be coherent. The hypothesis of superconductivity shows that there is a single, coherent, quantum mechanical wave function that decides the conduct of all the superconducting electrons. 

As an outcome, an immediate relationship can appear to exist between the speed of these electrons and the magnetic flux (Φ) encased within the superconductor.