Journal of Experimental and Theoretical Physics
 Journal of Experimental and Theoretical Physics
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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 paper improved.

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 inspiring.

D.E. Khmel'nitski, JETP Deputy Editor-in-Chief, Cavendish Laboratory, Univ. of Cambridge, the United Kingdom

The paper of L.P. Gor'kov "About the energy spectrum of superconductors"

2016-10-18 17:16:08

The presented paper of L.P. Gor'kov [1] [About the energy spectrum of superconductors'', Soviet Phys. JETP, 7, 505 (1958)] is one of the most important contributions to the theory of superconductivity after the papers, of Bardeen-Cooper, and Shrieffer (BCS) [2]. In these papers followed by the work of Bogoliubov [3], a microscopic theory of superconductivity was developed, but important conceptual questions remained not clarified.

The theory predicted a second-order phase transition to the superconducting phase, but the order parameter remained unknown. The physical meaning of the transition was not clarified. The relation to the very successful semi-phenomenological theory of Ginzburg and Landau was also not clear.

The methods used by BCS and by Bogoliubov apply to 'pure' superconductors. In the original form, they did not allow a direct generalization to problems related to the behavior of superconductors in  strong magnetic fields and were restricted by the weak-coupling approximation.

The work of Gor'kov [1] is based on a deep physical idea. The author realized that the transition to the superconducting state can be considered in a certain sense as the Bose-Einstein condensation of Cooper pairs. Instability with respect to formation of these pairs was discovered in the paper of Cooper [4] and the existence of the pairs is a basis of the theories of Bardeen-Cooper-Shrieffer [2] and Bogoliubov [3].

Go'rkov has shown [1] that  the condensation manifest itself analytically as the appearance of anomalous Green's functions of the type $\langle T(\psi(x_1))\psi(x_2)\rangle$ and $\langle T(\psi^{\dagger}(x_1))\psi^{\dagger}(x_2)\langle$ (cf. Eq.(5)) in the expansion of the two-particle Green's function. As follows from this and the subsequent Gor'kov's papers, the superconducting transition is characterized by the onset of an off-diagonal long-range order. The complex order parameter for this transition is the anomalous Green's function, more precisely, its value at coincident temporal arguments, which has the meaning of the wave function of a Cooper pair. In the weak-coupling model considered in the paper, the gap in the energy spectrum is proportional to the absolute value of this quantity. Gor'kov's equations are explicitly gradient invariant. In the previous formulations, this property was not obvious.

Subsequently Gor'kov has sown that close to the transition temperature, $ô_Ó$ his order parameter satisfies the Ginzburg-Landau equations, but the electron charge  $e$ has to be substituted by the Cooper pair charge $2e$ [5]. This substitution improved agreement with experiment.

Gor'kov's paper [1] was of great practical interest for researchers in the field.  Calculations in Gor'kov's formalism are much simpler than within the previous methods. In this three-page paper, not only an essentially new method is formulated but the energy spectrum and the specific heat are also found. Most important is that Gor'kov's technique allows deciding where the first approxmation is not sufficient and summation of an infinite number of terms is necessary. Gor'kov's equations have a convenient diagram interpretation. This allows selecting  the principle terms graphically and summing them.

A good example of the application of these possibilities is given by the famous joint papers of Abricosov and Gor'kov  on the theory of superconducting alloys [6]. It is impossible to list even the most important results obtained by this method.

It is worth mentioning that the paper of Gor'kov [1] is very well written and it is a pleasure to read it. Even now, after so many years, no single word in the paper has to be corrected; this is a generic property of classic works.

[1] L. P. Gor'kov, Soviet Phys. JETP 7, 505 (1958).

[2] J. Bardeen, L. N. Cooper, and J. R. Schrieffer, Phys. Rev. 106, 162 (1957); 108, 1175 (1957).

[3] N. N. Bogoliubov, Soviet Phys. JETP 7, 41 (1958).

[4] L. N. Cooper, Phys. Rev. 104, 1189 (1956).

[5] L. P. Gor'kov, Soviet Phys. JETP 9, 636 (1959).

[6] A. A. Abrikosov, L. P. Gor'kov, Soviet Phys. JETP 8, 1090 (1959); 9, 220 (1959).

L. P. Pitaevsky