# [SCI] BCS Superconductivity

**BCS Theory** (Bardeen, Cooper, Schrieffer, 1957) explains superconductivity — the zero-resistance, perfect-diamagnetic state of certain materials below a critical temperature — as a quantum condensate of paired electrons.

## Overview

Kamerlingh Onnes discovered superconductivity in mercury at 4.2 K (1911). Meissner and Ochsenfeld showed that superconductors expel magnetic fields (1933). The microscopic explanation came 46 years later: Cooper (1956) showed that any weak attractive electron–electron interaction (mediated by lattice phonons) causes electrons to form bound pairs (Cooper pairs). Bardeen, Cooper, and Schrieffer (1957) wrote the complete BCS theory showing the pairs condense into a macroscopic quantum state.

High-temperature superconductors (cuprates, Bednorz & Müller 1986; **Nobel 1987**) achieve Tc > 77 K. Superconducting magnets now enable MRI, particle accelerators, and quantum computers.

## Key Figures & Recognition

- **John Bardeen** (1908–1991), **Leon Cooper** (1930–), **Robert Schrieffer** (1931–2019): **Nobel Prize 1972** (Bardeen's second Nobel, having shared the first in 1956 for the transistor).
- **Georg Bednorz** (1950–) & **K. Alex Müller** (1927–2023): High-Tc superconductors. **Nobel Prize 1987**.

## Seminal Papers

- [Bardeen, J., Cooper, L. & Schrieffer, J.R. "Theory of Superconductivity." *Phys. Rev.* 108 (1957)](https://doi.org/10.1103/PhysRev.108.1175)
- Cooper, L. "Bound Electron Pairs in a Degenerate Fermi Gas." *Phys. Rev.* 104 (1956).

## What This Enables
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- **[TECH] MRI (Magnetic Resonance Imaging)** — High-field MRI magnets use NbTi or Nb₃Sn superconducting wire that remains viable only because BCS explains its properties.
- **[TECH] Quantum Computing Hardware** — Superconducting qubits (transmon, fluxonium) are based on Josephson junctions — a direct BCS/Andreev-reflection effect.
- **[SCI] Condensed Matter & Topological Physics** — BCS introduced Cooper pairs, the gap function, and macroscopic quantum coherence — concepts central to all of modern condensed matter.
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# Parents

* [SCI] Theory of Metals
* [SCI] Theory of Metals