Photo from the Nobel Foundation archive.
Lev Davidovich Landau
Born: 22 January 1908, Baku, Russian Empire (now Azerbaijan)
Died: 1 April 1968, Moscow, USSR (now Russia)
Affiliation at the time of the award: Academy of Sciences, Moscow, USSR
Prize motivation: "for his pioneering theories for condensed matter, especially liquid helium."
Prize share: 1/1
When certain substances are cooled to very low temperatures, their properties undergo radical changes. At temperatures a couple of degrees above absolute zero, helium becomes superfluid and the liquid flows without friction. One of Lev Landau's many contributions within theoretical physics came in 1941, when he applied quantum theory to the movement of superfluid liquid helium. Among other things, he introduced the concept of quasiparticles as the equivalent of sound vibrations and vortexes. This allowed him to develop his theoretical explanation for superfluidity.