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Portrait of Superconductivity

Science · Physics

Superconductivity

1911

Physics — condensed matter

The state in which certain materials lose all electrical resistance below a critical temperature and expel magnetic fields from their interior. Heike Kamerlingh Onnes discovered it in Leiden in 1911, when mercury cooled by liquid helium to 4.2 K abruptly lost its resistance. Walther Meissner and Robert Ochsenfeld found the field expulsion in 1933, and Bardeen, Cooper and Schrieffer explained it in 1957 with electrons bound into Cooper pairs. The 1986 discovery of ceramic materials working above the boiling point of liquid nitrogen transformed the field; it powers MRI scanners, the magnets of the Large Hadron Collider and maglev trains.

How to spot them

  • ▸Discovered in Leiden in 1911 when mercury was cooled with liquid helium to 4.2 K
  • ▸Zero electrical resistance, plus the expulsion of magnetic fields that makes a magnet float
  • ▸Explained in 1957 by three Americans whose initials name the theory
  • ▸The reason an MRI scanner and the LHC's magnets need cryogenic cooling

Key facts

Discovered in mercury at 4.2 K in Leiden, 1911, three years after the same lab first liquefied helium (1911)

Heike Kamerlingh Onnes, who won the 1913 Nobel Prize

The 1933 expulsion of magnetic flux that makes a magnet levitate above a cooled disc (1933)

The Meissner–Ochsenfeld effect

Explained in 1957 by three Americans whose surnames' initials gave the theory its three letters (1957)

Bardeen, Cooper and Schrieffer; Nobel Prize 1972

Electrons bound into pairs by lattice vibrations, named after the theorist who described them in 1956 (1956)

Cooper pairs, which behave as bosons and flow without scattering

The 1986 ceramic breakthrough that won a Nobel Prize the very next year (1986)

Bednorz and Müller's lanthanum barium copper oxide; the prize followed in 1987

The copper-oxide compound that in 1987 first worked above the boiling point of liquid nitrogen (1987)

YBCO, yttrium barium copper oxide, at about 92 K

Lanthanum hydride squeezed to 170 gigapascals held the record at about 250 K (2019)

LaH10, reported in Nature — warm, but only under immense pressure

Key ideas

  • Below the critical temperature, electrons pair up via distortions of the crystal lattice; the pairs condense into a single quantum state that cannot lose energy in small collisions, so current flows without resistance.
  • Expelling magnetic flux is not merely a consequence of zero resistance: it happens as the material cools through its transition even in a steady field, which is why it is a distinct effect.

Quick-fire facts

  • •Discovered by Heike Kamerlingh Onnes in Leiden on 8 April 1911, in mercury at 4.2 K; he won the 1913 Nobel Prize
  • •The Meissner effect — expulsion of magnetic flux — was found by Walther Meissner and Robert Ochsenfeld in 1933
  • •BCS theory (Bardeen, Cooper, Schrieffer, 1957) brought the 1972 Nobel Prize; it was John Bardeen's second, after the transistor in 1956
  • •Type II materials admit flux in quantised vortices; Abrikosov, Ginzburg and Leggett shared the 2003 Nobel Prize for that theory
  • •Georg Bednorz and Alex Müller found the first copper-oxide high-temperature material at IBM Zurich in 1986 and won the Nobel Prize in 1987, unusually fast
  • •YBCO (1987) works above 77 K, the boiling point of liquid nitrogen, making cheap cooling possible
  • •The best critical temperature at ordinary pressure is about 133 K, in a mercury-based cuprate; LaH10 reached roughly 250 K in 2019, but only under about 170 gigapascals
  • •A room-temperature superconductor remains unachieved, and several high-profile claims have been retracted
  • •Applications include MRI and NMR magnets, the Large Hadron Collider's dipoles, SQUID magnetometers and maglev trains
  • •A persistent current in a superconducting loop can circulate for years without measurable decay

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