Lev Landau developed descriptions of interacting quantum fluids through their elementary excitations. In the Landau critical velocity argument, creating an excitation of energy in flowing superfluid changes the relevant energy by . Requiring this to remain positive yields the ideal bound ; additional processes can limit actual flow at lower speeds.[ref]
The Theory of Superfluidity of Helium II by Lev Davidovich Landau. 1941 excitation-spectrum treatment; ideal flow criterion in modern notation
His Fermi liquid theory explains how strongly interacting fermions can retain long-lived low-energy quasiparticles, with interactions modifying their effective mass and collective response.[ref]The Theory of a Fermi Liquid by Lev Davidovich Landau. 1956 paper, introduction and energy as a functional of the distribution
A physicist.[ref]
https://kapitza.ras.ru/history/LDLandau/main.html. Independent professional profile
Portrait of Lev Landau
. Nobel Foundation; individual photographer unidentified. Commons PD-Sweden photograph designation; File requests a separate US public-domain tag. Not a worldwide clearance., via Wikimedia Commons. Source. Articles by others on the same topic
Lev Landau (1908–1968) was a prominent Soviet physicist who made significant contributions to many areas of theoretical physics, including condensed matter physics, quantum mechanics, and statistical mechanics. He is perhaps best known for his work in the theory of superfluidity and superconductivity, as well as for developing the Landau-Lifshitz series of textbooks, which are fundamental resources in theoretical physics.