Their names are in the history of the Institute

Natural talent as a teacher

Statistical physics and Condensed matter physics were studied at JINR with the arrival of N.N.Bogolyubov. In 1957, his articles "On a new method in the theory of superconductivity" were published and in 1959 - the paper of N.N.Bogolyubov and S.V.Tyablikov "Delayed and advanced Green's functions in Statistical physics" was published. These two topics were a red line in the scientific biography of Nikolay Maksimilianovich that arrived in Dubna in 1960 as a postgraduate of the Bogolyubov department.

In 1966, he became the first employee of the Sector of Statistical mechanics of BLTP under the supervision of Sergey Vladimirovich Tyablikov, one of Bogolyubov's best and closest students. After Tyablikov's untimely death in 1968, another close student of Bogolyubov, Dmitry Nikolaevich Zubarev became Head of the Sector. But soon, a struggle for part-time work started and in 1972, Dmitry Nikolayevich had to leave JINR. Since that time, Nikolay Maksimilianovich had been destined to become the carrier of the traditions and morals of Bogolyubov's scientific school in the field of Statistical physics. Almost all physicists from the Member States that came to JINR on the subject of Statistical physics communicated and worked with him, received advice and consultations. N. M. Plakida was the scientific core of the Sector.

Among many high quality papers of N.M., there are undoubtedly two great cycles that brought him worldwide fame. First of all, this is the theory of strongly anharmonic crystals developed by him and his co-workers. This theory allowed him to solve a very important problem for physics and practical applications: it explained the properties of crystals at high temperatures up to melting temperatures. However, it is more significant that this theory contained the method of irreducible Green's functions proposed by N.M. that is widely used by many authors nowadays. Using this method, Plakida and his co-workers managed to overcome basic difficulties in the theory of structural phase transitions concerning essentially nonlinear excitations and structural defects. These papers served as the basis for the monograph "Neutron scattering using ferroelectrics", published in 1984 and translated into English in 1990.

Superconductivity has a special place in N.M.'s activities that he became interested in as a student, when the foundations of this amazing phenomenon were laid at the Steklov Mathematical Institute and at JINR under the supervision of N.N.Bogolyubov. Even before the discovery of high-temperature superconductors (HTSCs), N.M. and his colleagues had started to study the impact of structural instability on the increase in superconductivity temperature. The final significance of this effect was finally confirmed in the joint work with N.N.Bogolyubov in 1988-1992. In recent years, N. M. developed the magnetic mechanism of HTSC. His profound knowledge of theory and experiment in Superconductivity physics made him a leading expert in this field, largely due to the basic monograph "High-Temperature Cuprate Superconductors", the second expanded edition of which was published in 2010 by Springer Publishers (Germany).

All investigations by N.M. were based on thorough analysis of experimental data, especially neutron data. The latter is due to the fact that from the very beginning the Sector was entrusted with the theoretical support of FLNP in condensed matter research. N.M. took this responsibility very seriously and took part in discussions of all significant experiments with which FLNP constantly "supplied" the Sector. It suffices to mention the long-term research on the IBR-30 and IBR-2 reactors of the role of Bose-Einstein condensation predicted by N.N.Bogolyubov in the superfluidity phenomenon and the research at the IBR-2 reactor of the structural peculiarities of HTSCs. Together with D.I.Blokhintsev, the mysterious problem of ultracold neutron leakage from traps was studied in the late 1970s.

Nikolay Maksimilianovich had a natural talent as a teacher. He started as an assistant in the Bogolyubov academic chair of Moscow State University and in Dubna D.I.Blokhintsev attracted him by giving lectures in his academic chair. It was a completely original course on the quantum theory of solids. He wrote a very informative textbook "Some problems in the quantum theory of solids", published at Moscow State University in 1974. But the regular work of the teacher did not attract him. I was still a graduate student when N.M. asked me to replace him during his business trips and in the early 1980s, he generally passed this course to me in the chair. Nikolay Maksimilianovich was attracted to education. We traveled together a lot and I often was amazed how he did not get tired of explaining the details of his work to everyone who wanted it an infinite number of times. At conferences and scientific schools, he was literally followed by crowds eager to get advice like a messiah. He generously shared his profound knowledge.

His fame as a scientist and educator has spread widely throughout the world. I have repeatedly been convinced that the words "I work with Plakida" has served as a password to enter the most elite scientific teams. Wherever you go, I mean the leading scientific centres, everywhere they know his classic works on the theory of strongly anharmonic crystals, the theory of phase transitions and the theory of superconductivity. Plakida's books can be found in libraries. Thanks to his scientific results, his active participation in numerous conferences, people in our country and in the world learned that high science had developed at JINR, not only in Particle and Nuclear physics, but also in Statistical physics. His name has been forever inscribed in the history of JINR, in the history of the world science.

The attitude towards science, students, life in general, his, I would say, classical intelligence, give grounds to rank Nikolay Maximilianovich among a pleiad of aristocrats of science.

Victor AKSENOV