Maarg Manthan · Topic 8.9

Superconductivity: History, Classification and Properties

Science & Technology › Physics – Mechanics, Waves and Thermodynamics · Topic 8.9

Superconductivity is a state in which certain materials lose all electrical resistance and expel magnetic fields when cooled below a critical temperature. It was discovered by the Dutch physicist Heike Kamerlingh Onnes in 1911, who found that the resistance of mercury dropped to zero at about 4.2 kelvin, close to absolute zero. Walther Meissner and Robert Ochsenfeld found in 1933 that a superconductor expels magnetic fields from its interior, called the Meissner effect, so a magnet can float above it. The BCS theory of 1957, by John Bardeen, Leon Cooper and Robert Schrieffer, explains conventional superconductors through pairs of electrons called Cooper pairs. In 1986 Georg Bednorz and Alex Muller found high-temperature ceramic superconductors that work above the temperature of liquid nitrogen.

5 min read · UPSC Prelims · Science & Technology · Physics – Mechanics, Waves and Thermodynamics

At a Glance

Discovered Kamerlingh Onnes, 1911 (mercury)
Key property Zero resistance
Meissner effect Expels magnetic field, 1933
BCS theory 1957; Cooper pairs
High-Tc ceramics 1986
Exam link UPSC Prelims, Science & Technology: Physics – Mechanics, Waves and Thermodynamics

Where Does It Fit?

This is the ninth topic of the macro on physics. It follows the topics on electromagnetism and heat, and sets up the next topic on applications. Previous topic: ionosphere Space…">Electromagnetic Wave Behaviour. Next topic: Applications of Superconductors.

What Is the History of Superconductivity?

Year	Milestone
1911	Onnes found zero resistance in mercury at about 4.2 kelvin after liquefying helium in 1908, and received the Nobel Prize in 1913
1933	Meissner and Ochsenfeld found the expulsion of magnetic fields, showing that superconductors are more than perfect conductors
1957	Bardeen, Cooper and Schrieffer gave the BCS theory, for which they received the Nobel Prize in 1972
1962	Brian Josephson predicted the Josephson effect, used in sensitive detectors
1986	Bednorz and Muller found a copper oxide ceramic superconducting at about 35 kelvin, and received the Nobel Prize in 1987
1987	Yttrium barium copper oxide worked at about 93 kelvin, above the boiling point of liquid nitrogen at 77 kelvin
2015	Hydrogen sulphide under extremely high pressure was reported superconducting at about 203 kelvin

What Are the Properties and Types of Superconductors?

Zero resistance: a current set up in a superconducting ring can flow for years without loss.
Critical temperature: the temperature below which a material becomes superconducting, such as 4.2 kelvin for mercury and 9.2 kelvin for niobium.
Critical magnetic field: a strong enough field or current destroys superconductivity.
Meissner effect: the interior of a superconductor is free of magnetic field, which allows magnetic levitation.
Type I superconductors: mostly pure metals such as lead, mercury and tin, with a sharp transition and a low critical field.
Type II superconductors: alloys and ceramics such as niobium-titanium and niobium-tin, which allow partial penetration of magnetic field as vortices, and can carry high current in strong fields. Used for magnets.
Cooper pairs: two electrons bound by lattice vibrations that move without scattering, in conventional superconductors.
Cooling: low-temperature types need liquid helium at about 4 kelvin, and high-temperature types can use cheaper liquid nitrogen.

What Else Should You Remember?

Room-temperature claims: no material is accepted to be a superconductor at ordinary temperature and pressure. The 2023 claim of LK-99 was not confirmed by other laboratories, and extreme pressure results need careful checking.
High-temperature superconductors: still work at very low temperatures, but are called high-temperature as they exceed 77 kelvin.
Iron-based superconductors: discovered in 2008, adding another family of materials.
Theory gaps: the BCS theory does not explain the ceramic superconductors, so their mechanism is an open question.
Related states: superfluidity in helium shows frictionless flow, as in States of Matter.
Materials in India: research on superconductors takes place at institutes such as the Tata Institute of Fundamental Research and IISc, and magnets for accelerators and fusion are built at institutions such as the Institute for Plasma Research.
Superconducting magnets: the Large Hadron Collider uses niobium-titanium magnets cooled to about 1.9 kelvin, as in Fundamental Particles and Basic Forces of Nature.
Cost: cooling, brittleness of ceramics and difficulty of making long wires limit use.
Link to electricity: ordinary resistance causes Joule heating losses, as in Concepts of Electromagnetism.
Zero resistance explained: in a normal metal, electrons scatter off lattice vibrations and impurities and lose energy, but in a superconductor the paired electrons flow through the lattice without scattering.
Josephson effect: the Josephson effect, in which current tunnels between two superconductors across a thin insulator, is used in very sensitive voltage and magnetic field detectors.
Magnetic levitation: a magnet floats above a superconductor because the superconductor expels its field, which is the principle behind some maglev train designs.

Why Does It Matter for the Exam?

History questions: who discovered superconductivity and when.
Concept questions: zero resistance, Meissner effect and levitation.
Current affairs link: claims of room-temperature superconductors and their verification.
Technology link: magnets for MRI, accelerators and fusion, as in the next topic.
Common errors: believing that superconductors work at room temperature or that Type I and II differ in resistance.

As an analytical point, superconductivity is a quantum effect on a visible scale. A room-temperature superconductor would change power and electronics, but none has yet been proved.

Why Is This Topic Important?

Facts Discovery and effect asked
Concept Types and BCS
News Room-temperature claims

What Came Next?

The next topic covers applications of superconductors. Next topic: Applications of Superconductors.

Key People and Terms

Critical temperature Temperature of onset of superconductivity
Meissner effect Expulsion of magnetic field
Cooper pair Bound pair of electrons
Type II superconductor Allows field vortices
Levitation Floating above a magnet
Liquid helium Coolant at 4 K

Exam Corner

Points to Remember

Onnes: 1911, mercury, 4.2 K.
Meissner effect: 1933.
BCS: 1957.
High-Tc: 1986, above 77 K.
LK-99 not confirmed.

Do Not Confuse With

Type I and Type II Pure metals with sharp transition versus alloys with vortices
Superconductor and perfect conductor Expels field versus only zero resistance
Liquid helium and liquid nitrogen 4 K versus 77 K coolants

Memory Hook

Onnes in eleven, mercury at four; Meissner expels the field, BCS pairs the electrons; eighty-six ceramics beat seventy-seven.

Mains Angle

Questions ask about the promise and limits of superconductors. These points add depth.

History Onnes to cuprates
Theory BCS
Limits Cooling and cost

A Question You May Face

An original practice question, not a past paper question.

“Explain superconductivity, its types and properties, and discuss the significance of high-temperature superconductors.”

How to Answer

Discovery Onnes.
Properties Zero R, Meissner.
Types I and II.
High Tc Ceramics.

GS Relevance

Prelims: discovery, Meissner effect, types, critical temperature, BCS theory, room-temperature claims. GS Paper 3: science and technology.

Frequently Asked Questions

What is superconductivity?

Superconductivity is a state in which a material loses all electrical resistance and expels magnetic fields when it is cooled below a critical temperature. Heike Kamerlingh Onnes discovered it in 1911 in mercury at about 4.2 kelvin, and it allows currents to flow without any loss of energy.

What is the Meissner effect?

The Meissner effect is the expulsion of magnetic fields from the interior of a superconductor when it is cooled below its critical temperature, discovered by Walther Meissner and Robert Ochsenfeld in 1933. It makes a magnet float above a superconductor, a demonstration of magnetic levitation, and shows that a superconductor is more than a perfect conductor.

What is the difference between Type I and Type II superconductors?

Type I superconductors are mostly pure metals such as lead and mercury, which lose superconductivity abruptly in a low magnetic field. Type II superconductors, such as alloys of niobium and ceramic cuprates, allow magnetic field to enter as vortices and stay superconducting in much stronger fields, so they are used to make powerful magnets.

What is the BCS theory?

The BCS theory, named after John Bardeen, Leon Cooper and Robert Schrieffer, explains conventional superconductivity of 1957. Electrons form pairs, called Cooper pairs, through interactions with vibrations of the crystal lattice, and these pairs move without scattering, which gives zero resistance, and the trio received the Nobel Prize in 1972.

Has a room-temperature superconductor been found?

No, no material has been proved to be a superconductor at ordinary temperature and pressure. Some claims, such as LK-99 in 2023, could not be reproduced by other laboratories, and reports of high superconducting temperatures in hydrides need extreme pressures, so the search for a practical room-temperature superconductor continues.

PYQ Practice — Statement Analysis

1 Superconductivity was discovered by Kamerlingh Onnes.

True

In 1911.

2 A superconductor has high electrical resistance.

False

It has zero resistance.

3 The Meissner effect is the expulsion of magnetic field.