BharatNotes What is Superconductivity?
Superconductivity is a state in which a material loses all electrical resistance and expels magnetic fields once cooled below a material-specific critical temperature (Tc). It was discovered in 1911 by Heike Kamerlingh Onnes, who observed the resistance of mercury drop to effectively zero at about 4.2 K (using liquid helium). Two defining hallmarks distinguish a superconductor from a merely "good" conductor: zero resistance (current can flow indefinitely without loss) and the Meissner effect (complete expulsion of magnetic flux), discovered in 1933.
How It Works — Key Concepts
The microscopic explanation for conventional (low-temperature) superconductors is the BCS theory (Bardeen–Cooper–Schrieffer, 1957; Nobel Prize 1972). Below Tc, electrons overcome their mutual repulsion and bind into Cooper pairs via interactions with lattice vibrations (phonons), forming a single coherent quantum state that flows without scattering.
Superconductors are classified into two broad types:
| Feature | Type-I | Type-II |
|---|---|---|
| Composition | Pure metals/metalloids | Alloys/compounds |
| Magnetic field | Fully expelled, single critical field | Partial penetration ("mixed/vortex state"), two critical fields |
| Critical temperature | Generally very low | Higher; more practical |
| Use in magnets | Limited | NbTi, Nb3Sn used in MRI, accelerators |
The High-Temperature Breakthrough
In 1986, Georg Bednorz and Alex Müller at IBM Zürich discovered superconductivity in a lanthanum-based copper-oxide (cuprate) ceramic at about 35 K, earning the 1987 Nobel Prize — the shortest gap ever between discovery and award. Soon after, YBCO (yttrium barium copper oxide) reached a Tc of about 93 K. This crossed a crucial threshold: it could be cooled with cheap liquid nitrogen (boils at 77 K) instead of expensive liquid helium, transforming the economics of the field.
Significance and Applications
Because they carry current losslessly and generate intense magnetic fields, superconductors enable several flagship technologies:
- Medical imaging — MRI machines use niobium-titanium (NbTi) superconducting magnets.
- Transport — superconducting maglev trains (notably Japan's system).
- Fusion energy — superconducting magnets confine plasma in tokamaks such as ITER.
- Particle accelerators — NbTi and Nb3Sn magnets steer beams at CERN's Large Hadron Collider.
- Quantum computing — superconducting circuits form qubits in machines from IBM and Google.
- Power transmission — lossless cables can cut grid energy losses.
Current Status and UPSC Angle
The "holy grail" is a room-temperature, ambient-pressure superconductor, which would revolutionise power grids and electronics. The much-hyped LK-99 claim (July 2023) was, by the scientific consensus reached in 2023–2024, not confirmed as a superconductor — the apparent levitation was traced to magnetic impurities. As of 2026, no ambient-pressure room-temperature superconductor has been validated; hydride materials show very high Tc but only under extreme pressures.
For UPSC, focus on the two hallmarks (zero resistance + Meissner effect), the discovery timeline, Type-I vs Type-II, the liquid-nitrogen significance of cuprates, and the strategic applications in energy, health and quantum technology.
