- Person
- Lev Landau
- Lived
- 1908–1968
- Field
- Theoretical Physics
- From
- Soviet
The story
Electrons in a metal repel each other strongly, so it was long a puzzle why simple models that ignored those interactions, treating the electrons as a free 'gas', worked so well. By the 1950s Lev Landau, head of the theoretical division at Moscow's Institute for Physical Problems, had already explained superfluid helium-4. In 1956 he turned to a related riddle and provided the answer.
His Fermi liquid theory starts from a thought experiment. Imagine a gas of non-interacting fermions, particles such as electrons that obey the Pauli exclusion principle, and slowly switch on the interactions between them. Landau argued that the system would change smoothly, so that each simple excitation of the gas becomes a corresponding excitation of the interacting liquid. These excitations, called quasiparticles, are dressed-up versions of the original particles: they carry the same charge and spin but behave as if they interact only weakly, often with a different effective mass. The theory explains why some properties of an interacting system closely resemble those of an ideal gas while others differ.
The theory applies most notably to the conduction electrons in ordinary metals and to liquid helium-3, a fluid whose atoms each contain an odd number of fermions and so behave as fermions themselves. It was developed further by Landau's students Alexei Abrikosov and Isaak Khalatnikov, using the diagrammatic methods of quantum field theory.
Fermi liquid theory has since been found to describe many other systems: the low-temperature behaviour of 'heavy fermion' materials, rare-earth alloys in which interactions make electrons behave as if they were many times heavier, and the low-energy interactions of protons and neutrons inside atomic nuclei. Its predictions can be tested directly with techniques such as angle-resolved photoemission spectroscopy.
The quasiparticle concept became one of the central ideas of modern physics, and Fermi liquid theory remains the standard starting point for understanding metals. Even strongly correlated materials such as strontium ruthenate, which resemble high-temperature superconductors, display key Fermi-liquid properties.
Why it matters
Landau's quasiparticle picture underpins the physics of metals and semiconductors on which electronics depends.
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.
- Lev Landau explained frictionless superfluid heliumLev Landau explained why liquid helium flows without friction below 2.17 K, introducing phonons and 'rotons'; it won him the 1962 Nobel Prize in Physics.
- 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
- Fermi liquid theory Wikipedia
- Lev Landau Wikipedia
- Lev Landau MacTutor History of Mathematics
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