Presentation Speech by Professor I. Waller, member of the Swedish Academy of Sciences
Your Majesties, Your Royal Highnesses,
Ladies and Gentlemen.
The winner of this year's Nobel Prize in Physics, Professor Lev
Davidovic Landau at Moscow University, was born in Baku, 1908. His
mathematical talents appeared at a very early age and at the age
of 14 he began his studies at the University of Leningrad. After
finishing them he spent one and a half years abroad, in
particular with the well-known atomic physicist Niels Bohr in Copenhagen. He made a
strong impression during this time thanks to his brilliant
intellect and great outspokenness.
In 1930 Landau published a quantum theoretical investigation
concerning the behaviour of free electrons in a magnetic field
which immediately gave him international fame. This work turned
out to be essential for the understanding of the properties of
metals. Starting from new fruitful ideas Landau found after his
return home, often in collaboration with his pupils, important
results concerning the structure of magnetic substances and
supraconductors and advanced fundamental theories for phase
transformations and thermodynamical fluctuations.
Landau's ability to see the core of a problem and his unique
physical intuition appear clearly in his investigations on liquid
helium which he started after having been attached in 1937 to the
Institute for Physical Problems in Moscow. The head of this
institute was the famous physicist Kapitsa who then
performed interesting experiments on liquid helium. The natural
helium gas had earlier been liquefied by cooling to about four
degrees above the absolute zero of temperature and subsequent
research had shown that this fluid when further cooled about two
degrees was transformed to a new state which has quite strange
properties. According to a term introduced by Kapitsa it is
superfluid which means that it can easily flow through very fine
capillaries and slits which almost completely prevent the flow of
all other liquids.
The originality in Landau's attack on the problem of explaining
these phenomena was that he considered the quantized states of
motion of the whole liquid instead of the states of the single
atoms as other scientists had done earlier. Landau started by
considering the state of the fluid at the absolute zero
temperature which is its ground state. He described the excited
states of the liquid by the motion of certain fictive particles
called quasiparticles. Landau combined experimental results with
his calculations and deduced in this way the mechanical
properties of the quasi-particles. These results, from which the
properties of the fluid could be calculated, were later directly
confirmed by investigations on the scattering of neutrons in
liquid helium. Such experiments were first performed at Atomic
Energy Ltd. in Stockholm in 1957. Landau further found that there
exists in liquid helium besides ordinary sound waves also waves
of a "second sound". He inspired thereby a Russian scientist to
confirm this phenomenon experimentally.
Natural helium consists of an isotope of atomic weight 4 apart
from about one millionth of another isotope of atomic weight 3.
The lighter isotope has been studied in the liquid state since
about 1950. This kind of liquid helium has properties which are
quite different from those of the heavier isotope because the
helium nuclei of atomic weights 3 and 4 are essentially
different. A satisfactory theory for the lighter helium liquid
was first given by Landau in 1956 - 1958 and has many formal
similarities with his above-mentioned theory for the heavier
isotope. The new theory is valid only at very low temperatures,
less than one tenth of a degree above absolute zero. This is,
however, the most interesting temperature range. Due to the
difficulty of making measurements at these low temperatures the
theory was not experimentally tested until very recently. These
tests have been the more favourable for the theory the more the
measuring technique has been refined. Landau has also predicted a
new kind of wave propagation for this liquid and has called it
zero sound. He has thereby stimulated experimental scientists to
great efforts aiming to detect zero sound.
The importance of Landau's investigations are apparent when one
considers that an important goal of physics research is to
explain the properties of liquids as completely as it has been
possible to explain the properties of crystals and of rarefied
gases. In their efforts to attain this goal the scientists have
in general met with insurmountable difficulties. An essential
exception is Landau's theories of liquid helium which therefore
are an achievement of great and profound importance.
Besides his investigations on condensed matter, i.e. matter in
the solid and liquid state for which he is now awarded the Nobel
Prize, Landau has also made contributions of the utmost
importance to other parts of physics, in particular to the
theories of quantized fields and of elementary particles. He has
by his original ideas and masterly investigations exercised
far-reaching influence on the evolution of the atomic science of
our time.
Professor Landau has unfortunately not yet fully recovered from
the severe accident which he sustained at the beginning of this
year. He is therefore not here to receive his Nobel Prize which
is instead handed to him today by the Ambassador of Sweden in
Moscow. On behalf of the Swedish Academy of Sciences I wish to
express the hope that Professor Landau will soon completely
recover.
From Nobel Lectures, Physics 1942-1962, Elsevier Publishing Company, Amsterdam, 1964
Copyright © The Nobel Foundation 1962