JETP Golden Pages
Browsing Old Pages
The Editorial Board decided to establish a new page at the
web-site of JETP, where today reader could find the best papers
published by our journal in the past. JETP
GOLDEN PAGES. Our aim is simple: the potential reader and
potential author might be inspired by reminding about the glorious
past. Selecting classical papers, the editors experienced
considerable difficulty: so many excellent articles "competed"
for a place at Golden Pages. Making our choice, we did not use
formal criteria, relying mainly on the expertise of those, who were
reading and writing to JETP in its most successful time.
Under the name Journal of Experimental and Theoretical Physics
(JETP) our journal is known to the Russian readers since 1931. In
July 1955, American Institute of Physics sent to subscribers the
first issue of its new publication Soviet Physics JETP. It contained
the English translation of the January 1955 issue of the Journal of
Experimental and Theoretical Physics. Soviet Physics JETP and later
JETP continues to appear monthly ever since, giving to international
readership an easy access to the results of research in physics in
Soviet union and later in Russia. Having in mind not only
Russian-speaking audience, we limited our search to the best papers,
which were published after 1954. Fortunately, this was the time of
a upturn in Soviet Physics. By that time, JETP was nearly
unique journal on physics in Soviet union [The time, when the new
specialized journals: Plasma Physics, Nuclear Physics, Solid State
Physics and a separated JETP Letters - were created, was 5-10 years
ahead]. So, it received the whole outburst of new results of
research in physics. Browsing the pages of JETP in 1950th, the
reader finds a great number of publications of the papers on
fundamental physics, which were not published earlier, because their
authors were involved in a classified research and were not allowed
to publish anything in open journals. This added to the great
density of high quality publications in JETP. In 1955, there were no
single winner of the Nobel Prize in Physics in Soviet union. The
awards to I.E. Tamm, I.M. Frank and P.A.Cherenkov, N.G. Basov and
A.M. Prokhorov, L.D. Landau, P.L. Kapitza, Zh.I. Alferov, V.L.
Ginzburg and A.A. Abrikosov were all in the future. But the Nobel
Prize winning publications for many of them were about to appear at
the pages of JETP.
1955 was also the year, when P.L. Kapitza was appointed the
Editor-in-Chief of JETP. He remained in this post till his death in
March 1984, holding the problems of the journal in the center of his
attention. The Editorial office moved to the grounds of the Kapitza
Institute for Physical Problems. Since that time, a unique climate
of the Kapitza Institute was extended to the Editorial office.
One of the first action of Kapitza's in JETP was an appointment of
E.M. Lifshits the Deputy Editor and passing on him the major
responsibility of day-to-day operation of the journal. E.M. remained
the guiding spirit of the journal for 30 years till his death in
1985. Everybody, who visited the Editorial office in those days,
remembers E.M. sitting in the first room, reading the manuscripts or
writing the letters. His lightning reaction to every paper is still
memorable to all those, who experienced these reactions or read his
letters to the authors. The whole style of the journal, the balance
of more specialized articles and those of a general significance,
the dominance of the original results over the criticism of the
works of the colleagues - all this was established in those days
under watch of E.M. It would not be an exaggeration to say, that
E.M. strongly influenced the style of writing about physics in
Russian through both 10 volumes of the Course of Theoretical Physics
and his 30 years as the Deputy Editor of JETP.
Moving further to publications of 1960-1975, the reader finds out
considerable changes. First of all, the reader finds here new names.
New generation of physicists, those, who obtained their education in
the after-war time, arrived at the front line of research. Secondly,
establishing of new specialized journals reduced the number of
articles published in JETP and devoted to very special aspects of
particular branches of physics. JETP becomes the journal to report
about the results interesting to all physicists. The short Letters
to the Editor disappear from the pages of our journal. This is
because, thanks to the initiative of A.S. Borovik-Romanov, new JETP
Letters started to publish short articles in a separated journal [A.S.
loved to call it a physical newspaper]. Still, the volume of
each monthly issue of JETP increases after 1960. What is remarkable
about these years, that the professional quality of even ordinary
Browsing today the pages of the old issues of our journal, any
reader gets excited by coming across a great number of papers,
which became an absolute classics. Often, the classical papers
follow one another. A GOLDEN AGE. We expect
that the readers and the authors will enjoy visiting new pages
at web-site of JETP. In the end of the days, the classical papers
are classical just because they are so useful to read them and so
D.E. Khmel'nitski, JETP Deputy Editor-in-Chief, Cavendish Laboratory, Univ. of Cambridge, the United Kingdom
Properties of the spectrum of elementary excitations near the disintegration threshold of the excitations (JETP paper by L. P. Pitaevskii)
Download as PDF
In his 1959 JETP article [Properties of the spectrum of elementary excitations near the disintegration threshold of the excitations, JETP 36, 830 (1959)], Lev Pitaevskii theoretically investigated the quasiparticle decays and related singularities appearing in the excitation spectra of Bose liquids. Specifically, he was interested in the two-roton decay processes, which exist in liquid helium, the only quantum Bose liquid known at that time. The remarkable shape of the excitation spectrum of the superfluid 4He with continuously connected phonon and roton branches was suggested in a short note by L. D. Landau in 1947 . It took another decade before the first observation of rotons was achieved in the inelastic neutron scattering experiments by Palevsky and collaborators . Landau’s main motivation was to explain the anomalous hydrodynamic and thermodynamic properties of the superfluid state. Accordingly, Landau did not concern himself with the details of the dispersion curve for high-energy excitations, which make a negligible contribution into the thermodynamics below the superfluid transition temperature Tc = 2.17 K. Neutron-scattering techniques rapidly developed in the 1950’s and 1960’s provided a powerful tool to study physics of high-energy excitations in quantum liquids.
Scattering processes with nonconserving quasiparticle numbers may appear in the superfluid state because of particle exchange with the Bose condensate and, generally, require presence of certain broken symmetries, as the gauge symmetry breaking in the superfluid state. The self-energy correction to the boson Green’s function determined by two-particle decays turns out to be singular near the decay threshold. Analyzing the energy and momentum conservation laws, Pitaevskii classified all such singularities in three dimensions and for the case of roton decays predicted the termination or end point on the dispersion curve ε(p) at the energy equal twice the roton gap. This theoretical prediction stimulated a lot of experimental studies on the dynamic properties of liquid helium using neutron, X-ray, light scattering, and ultrasonic techniques. The experimental efforts culminated in the direct observation of the end point in the spectrum of liquid 4He .
As was emphasized by Pitaevskii himself, the obtained results are not restricted to liquid helium but may apply to other condensed matter systems with bosonic excitations. These include, for example, phonons in anharmonic crystals and cold atomic gases in optical traps. Recently, similar effects have been predicted and experimentally studied for magnons in quantum antiferromagnets . Different magnetic materials provide various magnon dispersion laws ε(p) with one-, two-, or three-dimensional character leading to new spectacular effects, which are most prominent in low dimensions. For many decades condensed matter theorists were preoccupied with singularities that arise due to phase transitions, strong correlations, and many-body effects. The first effect of such type in quantum Bose systems was predicted by Pitaevskii in 1959.
 L. D. Landau, J. Phys. USSR 11, 91 (1947).
 H. Palevsky, K. Otnes, K. E. Larsson, R. Pauli, and R. Stedman, Phys. Rev. 108, 1346 (1957); H. Palevsky, K. Otnes, and K. E. Larsson, Phys. Rev. 112, 11 (1958).
 B. Fåk and J. Bossy, J. Low Temp. Phys. 112, 1 (1998); H. R. Glyde, M. R. Gibbs, W. G. Stirling, and M. A. Adams, Europhys. Lett. 43, 422 (1998).
 M. E. Zhitomirsky and A. L. Chernyshev, Rev. Mod. Phys. 85, 219 (2013).
Dr. M. E. Zhitomirsky,
staff scientist, Commissariat à l'Énergie Atomique, Grenoble, France