- Person
- Lev Landau
- Lived
- 1908–1968
- Field
- Theoretical Physics
- From
- Soviet
The story
Water freezing, iron becoming magnetic, a metal turning superconducting: all are phase transitions, changes in the state of matter. Some, like boiling, happen abruptly. Others, called continuous or second-order transitions, happen smoothly, with the material's properties changing gradually as it passes a critical temperature. In the 1930s, when Lev Landau was building his school of theoretical physics in Kharkiv and Moscow, there was no general way to describe them.
Landau proposed one. He suggested that each transition could be described by an order parameter, a quantity that is zero in the disordered state above a critical temperature and becomes non-zero below it, such as the overall magnetisation of a magnet. He then argued that near the transition the energy of the system must depend smoothly on the order parameter and must respect the symmetries of the material. Writing the energy as a simple expansion in powers of the order parameter, he could predict how a material's properties change near the transition.
The theory captured a deep idea: a phase transition is often a change of symmetry, in which an ordered state breaks a symmetry that the disordered state possesses. Landau's approach could also be adapted to systems in external fields and used as a model for abrupt transitions. Vitaly Ginzburg, Albert Devonshire and others later extended it, and in 1950 Ginzburg and Landau applied it to superconductors.
Physicists later found that the theory predicts some details incorrectly, such as the exact critical exponents of magnets and liquid-gas systems, and these were refined using the renormalisation group and scaling theory. Even so, Landau theory remains an exceptionally broad and powerful framework, and the concept of the order parameter has proven transformative.
The ideas of the order parameter and broken symmetry spread from magnets and crystals to superconductors, superfluids, liquid crystals and even particle physics. Landau theory is a standard part of every physicist's training, and it remains a natural starting point whenever researchers meet a new phase of matter.
Why it matters
Landau's framework is taught to physics students everywhere and guides the design of new materials, from magnets to superconductors.
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.
- 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.
Sources
- Landau theory Wikipedia
- Lev Landau Wikipedia
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