The theory of superconductivity came into existence in the year 1911 when the temperature of mercury was nearly 40C by the physicist Onnes for which he won the Nobel prize. From then, the concept of superconductivity progressed, and various kinds of superconductors were discovered. Later on, with many inventions, superconductors also tend to function even at higher temperature levels.
The invention of high-temperature kind of superconductors reached multiple domains and the whole domain contributed to the commercial progress and research of these substances. And now, this article completely discusses what is a superconductor, its types, functionality with few examples.
What is Superconductor?
Superconductors are considered substances that conduct electricity even without resistance. This represents that superconductors hold the ability to carry currents without losing energy which is the main advantage of this when compared with traditional type conductors.
The utilization of superconductors in magnetic substances is restricted by the truth that strong magnetic fields ahead of the specific critical value based on the substance trigger a superconductor to get back to its original state even when the temperature is below the transition level. In general, the conductor’s temperature gets decreased when there is an increase in conductivity level whereas in superconductors after some specific level of temperature, the resistance gets down to ‘0’, and the conductivity gets to a maximum value.
In the superconductors, the material’s conductivity becomes so that when there is the passage of current through the device, then there will be an indefinite flow of current having no necessity of any power supply. This directs to the development of energy sources that are self-sustained so that it solves many issues like high-end electricity and power fluctuations.
And also, as there will be no energy loss because of the material’s resistivity and the electricity will be available at minimal prices when those superconducting substances are utilized as power sources.
Superconductor Types
There are mainly two types of superconductors which are explained as follows:
- Type I
- Type II
Type I Superconductors – These types of superconductors function as conductors when operated at room temperatures, whereas when they are cooled below the temperature of Tc, the molecular movement present inside the substance decreased so that the current flow can go as unobstructed.
Type II Superconductors – These are not very good conductors operated at room temperature, then switch to a superconductor type is somewhat more when compared with type I superconductors. These types of substances are generally used as alloys and as metallic substances.
The below tabular column clearly shows the comparison between the above types of superconductors:
| Type – I | Type – II |
| These are also termed low-temperature superconductors | These are also termed high-temperature superconductors |
| These have a low critical magnetic field which lies in the range between 0.0000049T to 1 tesla | This type of device operates under high critical magnetic field which is above 1 tesla |
| The performance of superconductivity can be easily lost because of the minimal intensity magnetic field. So-called soft superconductors | The performance of superconductivity cannot be easily lost because of the external intensity magnetic field. So-called high superconductors |
| These are totally diamagnetic substances | These are no diamagnetic substances |
| There will be no existence of the mixed state | A mixed state exists in these superconductors |
| Minimal impurity levels show no effect on superconductivity | Even minimal impurity levels show the effect on superconductivity |
| Using the approach of BCS, the superconductivity nature of these substances can be explained easily | The superconductivity of type-II superconductors cannot be explained using BCS theory |
| These substances completely abide by the guidelines of the Meissner effect and magnetic field cannot saturate into the substance | Type II materials to some extent abide by the Meissner effect so there will be the chances of magnetic material entering into the substance |
| The shift from superconducting to normal state is intense because of external magnetic impact | The shift from superconducting to normal state is not intense and not abrupt too. At the condition of the less magnetic field, these substances start to lose their superconductivity nature and at higher magnetic fields, they completely lose the behavior. |
| Examples of Type-I are Lead, Hg, Zn, and others | Examples of Type II are NbTi and others |
Properties
The superconducting materials show various unique properties and so those are extensively used in various applications. A few of the properties of superconductor are explained below:
Critical Current – When there is the passage of electric current across the superconducting substance, there will be magnetic field development. When the current value exceeds a specific limit, the magnetic field raises to the maximum value where the conductor reaches the regular state. And this is termed as critical current.
Josephson Current – When the separation of two superconductors takes place by a thin insulating substance forming a junction with minimal resistance, it was observed that copper pairs (which are developed because of phonon contact) of electrons, might be able to move from one junction to another. The current that happens because of cooper pairs flow is termed as Josephson current.
Persistent Current – When a ring is created using a superconductor and it is placed in the vicinity of the magnetic field beyond the level of critical temperature, and now when the ring is cooled lower than the critical temperature level and when the magnetic field is removed, then there happens induction of current in the ring because of its self-inductance.
Using Lenz law, the induced current direction is in the path that contradicts the variation in flux that flows through the ring. As the ring holds superconducting behavior, the induced current in the ring persists to flow and this is termed as persistent current. This current created a magnetic flux that allows the magnetic flux to move through the ring constantly.
Infinite Conductivity – When a material is in the superconducting state, the substance exhibits zero electric resistance called infinite conductivity. And when some piece of this substance is cooled minimal to its critical temperature value, the resistance drops abruptly to ‘0’. For instance, the zero resistance value of mercury happens below the level of 4k.
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Transition Temperature – For a superconducting substance, the critical temperature is termed the temperature level where the substance moves from the normal conduction phase to the superconducting phase. This movement between the two phases is completely abrupt and sharp. The below picture shows the transition between phases for mercury.
Superconductor Critical Temperature
Critical Magnetic Field – For a superconducting substance, it loses its behavior when the magnetic field extends above a specific value and then the material starts to function as an ordinary type of conductor. And the specific value where the superconductor gets back to its normal state is termed a critical magnetic field. This is based on temperature.
Critical Magnetic Field
When the critical temperature decreases, the critical magnetic field value arises, and this phenomenon is shown in the below picture.
Meissner Effect – When a superconducting substance is allowed to cool down below the level of critical temperature, then it ejects the magnetic field and does not allow for the penetration of the magnetic field inside it. This scenario is termed as Meissner effect.
Semiconductor V/S Superconductor
The foremost difference between a semiconductor and a superconductor is in electrical conductivity. For semiconductors, the electrical conductivity lies in the range between insulator and conductor. For superconductors, the electrical conductivity is more than the conductor.
Also, the band distance for semiconductors is 0.25 eV – 2.5 eV and for superconductors, it is more than 2.5eV.
| Semiconductor | Superconductor |
| These substances have finite resistivity | For superconductors, the resistivity is zero which means zero electrical resistivity |
| Semiconductors do not exhibit complete diamagnetism | Superconductors exhibit excellent diamagnetism properties |
| Here, electronic repulsion directs to the resistivity of finite range | Here, electronic attraction directs to failure in resistivity |
| Flux quantization in semiconductors is nearly 2e units | The superconductor unit is e |
| The energy gap for semiconductor materials lies in the range of a few eV | The energy gap for superconductor materials lies in the range of 10-4eV |
Superconductor Examples
The best examples of a superconductor include the follwoing.
Aluminum
We are aware that aluminum is an excellent conductor at room temperature levels. But also, it is a good superconductor where it becomes Type-I at 1.2K and the resistivity suddenly reduces to ‘0’.
Niobium – tin
This is an intermetallic substance of both tin and niobium compounds where the formula is Nb3Sn. This is utilized as a type II superconductor for the creation of superconducting electromagnets, wiring substances, and solenoids.
ReBCO
ReBCO is Rare Earth Barium Copper Oxide which comes under the group of chemical substances that have extended excellent superconducting nature. Superconductors that are developed using ReBCO hold the capability to tolerate extended magnetic fields compared with other superconductors.
Applications
A few of the applications of superconductors are explained below:
- These are utilized for particle acceleration in huge hadron colliders
- SQUID substances are implemented in the production of very sensitive magnetometers which are used for finding land mines
- Magnets those are with superconducting behavior are implemented in MRI equipment’s
- To get rid of power loss, ordinary kind cables are replaced with superconducting cables
- Superconducting substances are even employed in EMP’s which have extended intensity levels
- Even maglev trains function on the superconducting phenomenon
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So, this is all about the detailed explanation of superconductors. This article has provided information on superconductor types, examples, their properties, and applications. Furthermore, know what are the real-life applications of superconductors?