Superconductor

A superconductor is a material that attains superconductivity, a state of matter with no electrical resistance. In a superconductor, an electric current can persist indefinitely. This article will familiarise you with the concept of superconductors.

What is a Superconductor?

Superconductors are different from ordinary conductors, such as copper. Unlike regular conductors whose resistance gradually reduces, the superconductor’s resistance drops to zero below a fixed temperature, which is the critical temperature. At this temperature, a superconductor can conduct electricity with no resistance, which means no heat, sound, or other forms of energy would be discharged from the material when it reaches the “critical temperature” (Tc). To become superconductive, most materials must be in an incredibly low energy state (very cold). Presently, excessive energy must be used in the cooling process, making superconductors uneconomical and inefficient. A study is underway to design compounds that become superconductive at higher temperatures.

Superconductor Definition

“A superconductor is defined as a substance that offers no resistance to the electric current when it becomes colder than a critical temperature.”

Some of the popular examples of superconductors are aluminium, magnesium diboride, niobium, copper oxide, yttrium barium and iron pnictides. These substances superconduct at temperatures below the critical temperature.

Critical Temperature for Superconductors

The critical temperature for superconductors is the temperature at which the electrical resistivity of metal falls to zero. Most materials show superconducting phase transitions at low temperatures. The highest critical temperature was about 23 K until 1986. In 2020, a room-temperature superconductor made from carbon, hydrogen and sulfur under pressures of around 270 gigapascals was identified to possess the highest temperature at which any material has shown superconductivity.

The table below lists the critical temperature for various materials

Superconductor Working

When the temperature of the metal decreases below the critical temperature, the electrons in the metal form bonds known as Cooper pairs. The electrons can’t offer any electrical resistance when bonded like this—allowing electricity to flow through the metal smoothly.

Nevertheless, this only works at low temperatures. When the metal gets warm, the electrons gain enough energy to break the bonds of the Cooper pairs and go back to offering resistance.

Superconductor Graph

The below graph shows the temperature dependence of the electrical resistivity of normal metal and a superconductor.

A graph of conductor and superconductor resistance plotted against temperature.

Superconductor Types

Superconductors come in two distinct types: type I and type II.

Type I Superconductors

A type I superconductor consists of fundamental conductive elements that are used in everything from electrical wiring to computer microchips. Presently, type I superconductors have critical temperatures between 0.000325 °K and 7.8 °K. A few of the type I superconductors need tremendous amounts of pressure in order to achieve the superconductive state. One such material is sulfur, which needs a pressure of 9.3 million atmospheres (9.4 x 10¹¹ N/m²) and a temperature of 17 °K to reach superconductivity. Approximately half of the elements in the periodic table are superconductive.

Type II Superconductors

A type II superconductor comprises metallic compounds such as lead or copper. They achieve a superconductive state at much higher temperatures compared to type I superconductors. Type II superconductors can be penetrated by a magnetic field, whereas type I cannot.

​​Superconductor Properties

The superconducting materials exhibit some unique properties necessary for current technology. The research on these properties is still going on to utilise these properties in various fields. The four most important properties of superconductors are listed below:

Infinite Conductivity

A material has zero resistance in the superconducting state. When the temperature of the material is below the critical temperature, its resistance abruptly lowers to zero. For example, Mercury shows zero resistance below 4 kelvin.

Critical Temperature

The critical temperature is the temperature below which the material changes from conductors to superconductors. The critical temperature is also called transition temperature. The transition from conductors to superconductors is sudden and complete.

Magnetic Field Expulsion

When a material transitions from the normal to the superconducting state, it expels magnetic fields from its interior; this is called the Meissner effect.

Critical Magnetic Field,

The value of the magnetic field beyond which the superconductors return to conducting state, is known as the critical magnetic field. The value of the critical magnetic field is inversely proportional to the temperature.

Superconductor Applications

• Superconductors are used in particle accelerators, generators, transportation, computing, electric motors, medical, power transmission, etc.
• Superconductors are primarily employed for creating powerful electromagnets in MRI scanners.
• These conductors are used to transmit power for long distances.
• They are used in memory or storage elements.

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