- Person
- Lev Landau
- Lived
- 1908–1968
- Field
- Theoretical Physics
- From
- Soviet
The story
In 1937 Pyotr Kapitsa in Moscow, and independently John Allen and Don Misener, discovered that liquid helium cooled below about 2.17 degrees above absolute zero behaves bizarrely. It flows without any friction, slips through the tiniest pores and can even climb up the walls of a beaker and out over the rim. Nobody could explain this 'superfluid' behaviour.
Lev Landau, born to a Jewish family in Baku and one of the most brilliant theorists of his generation, was then head of the theory division at Kapitsa's Institute for Physical Problems. In April 1938 he was arrested by Stalin's secret police for his connection with a leaflet denouncing the regime, and he spent a year in the Lubyanka prison. Kapitsa courageously wrote to Stalin, personally vouched for Landau and threatened to quit unless he was freed. Niels Bohr wrote too, and in April 1939 Landau was released.
Soon afterwards he took up Kapitsa's puzzle. In 1941 he published a theory that treated the liquid as a quantum system whose motion is carried by collective excitations: sound waves, or phonons, and a further kind of excitation he called the roton, whose energy spectrum he refined in 1947. The theory explained why the liquid could flow without losing energy. It also predicted a strange new phenomenon, a temperature wave called 'second sound', and three years later experiments in Moscow confirmed that it exists.
In 1962 Landau received the Nobel Prize in Physics for his pioneering theories for condensed matter, especially liquid helium. He could not travel to Stockholm, because in January that year he had been gravely injured in a car accident. Kapitsa himself received the Nobel Prize in 1978 for his low-temperature discoveries.
Landau's work, developed further with his student Isaak Khalatnikov, remains the accepted macroscopic theory of superfluidity in helium-4. Physicists have since probed the roton spectrum of helium with techniques such as microwave and Bragg spectroscopy, and in 2018 rotons were also detected in an ultracold Bose-Einstein condensate.
Why it matters
Landau's approach of describing matter through its collective excitations became a cornerstone of modern condensed-matter physics.
About Lev Landau
Baku-born prodigy who founded the great Soviet school of theoretical physics, survived Stalin’s prison, explained superfluid helium and won the 1962 Nobel Prize.
More about Lev Landau
- Lev Landau predicted a strange way plasma waves fadeIn 1946 Lev Landau predicted that waves in a plasma can lose energy without any collisions, an effect confirmed experimentally in 1964 and now called Landau damping.
- Landau co-discovered the quantum density matrixIn the late 1920s, while still a teenager, Lev Landau independently introduced the density matrix, a basic tool of quantum physics, alongside John von Neumann.
- Landau's Fermi liquid theory explains metalsIn 1956 Lev Landau introduced Fermi liquid theory, explaining why electrons in metals and atoms in liquid helium-3 behave almost like free particles.
- The Ginzburg–Landau theory explains superconductorsLev Landau and Vitaly Ginzburg created the Ginzburg–Landau theory of superconductivity, work that helped win Ginzburg and Landau's student Abrikosov the 2003 Nobel Prize.
- Landau levels underpin the quantum Hall effectIn 1930 Lev Landau showed that electrons in a magnetic field occupy discrete energy levels, now called Landau levels, key to explaining the quantum Hall effect.
- Landau and Lifshitz wrote physics' great textbook seriesWith his student Evgeny Lifshitz, Lev Landau began the ten-volume Course of Theoretical Physics, still used by graduate physics students worldwide.
- Landau's 'Theoretical Minimum' trained a generationLev Landau's famous 'Theoretical Minimum' exams, passed by only 43 candidates from 1934 to 1961, created the Soviet Union's greatest school of theoretical physics.
- Landau's theory explains how matter changes stateLev Landau's theory of second-order phase transitions introduced the 'order parameter', still a broad and powerful framework for how matter changes state.
Sources
- Lev Landau Wikipedia
- Lev Davidovich Landau MacTutor History of Mathematics, University of St Andrews
- Superfluidity Wikipedia
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