= Lev Landau
{c}
{wiki}
= Lev Davidovich Landau
{c}
{synonym}
= L. D. Landau
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{synonym}
<Lev Landau> developed descriptions of interacting quantum fluids through their elementary excitations. In the <Landau critical velocity> argument, creating an excitation of <energy> $\epsilon(\mathbf p)$ in flowing <superfluid> changes the relevant energy by $\epsilon(\mathbf p)-\mathbf v\cdot\mathbf p$. Requiring this to remain positive yields the ideal bound $v_c=\min_p\epsilon(p)/p$; additional processes can limit actual flow at lower speeds.<The Theory of Superfluidity of Helium II by Lev Davidovich Landau>[1941 excitation-spectrum treatment; ideal flow criterion in modern notation]{ref} 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.<The Theory of a Fermi Liquid by Lev Davidovich Landau>[1956 paper, introduction and energy as a functional of the distribution]{ref}
A <physicist>.https://kapitza.ras.ru/history/LDLandau/main.html[Independent professional profile]{ref}
\Image[https://commons.wikimedia.org/wiki/Special:Redirect/file/Landau.jpg?width=250]
{title=Portrait of <Lev Landau>}
{description=Nobel Foundation; individual photographer unidentified. https://commons.wikimedia.org/wiki/File:Landau.jpg[Commons PD-Sweden photograph designation; File requests a separate US public-domain tag. Not a worldwide clearance.], via Wikimedia Commons.}
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