A. F. Ioffe

A. F. IOFFE

(On His Sixtieth Jubilee)

I. K. Kikoin, Sverdlovsk

Academician Abram Fedorovich Ioffe deservedly enjoys exceptional popularity in our country not only among physicists (which is quite natural), but also among broad strata of workers, the intelligentsia, and students.

A. F. is widely known not only as the author of major scientific investigations and discoveries, but also as an outstanding organizer of Soviet physics.

His invaluable merit consists in the fact that he succeeded in raising physical science in our country to a height it had never before attained. He was able to arouse interest in the physical sciences among a large group of his pupils, and this gave him the possibility, in a comparatively short time, to create a large collective of physicists, which is continuously growing both qualitatively and quantitatively. The Physico-Technical Institute, created and unfailingly directed by him, from the very beginning and to this day has been the center of attraction for all physicists engaged in and interested in science. To work in the Institute headed by A. F. Ioffe has always been, and is considered, a great honor.

Perhaps an even greater merit of A. F. is that he and his pupils managed to instill an interest in physics among industrial workers. Now, after a number of years of work by the collective of physicists on major technical problems, industrial workers have realized what possibilities physics possesses for improving and substantially changing production processes, and we are already witnesses to the joint fruitful work of physicists and production workers. The work of A. F. Ioffe himself and of his closest pupils contributed to this to a considerable degree.

One could cite many examples of the fruitful work of physicists in various branches of industry. But perhaps the most striking example is the work of the Physico-Technical Institute in the field of the rubber industry. Until then the rubber industry had been considered the most remote from physics; it was regarded as a purely chemical industry. But the work

The Institute’s work in the study of the structure of amorphous bodies showed that physics could introduce a number of substantial improvements into the technology of manufacturing synthetic rubber. At first it was necessary to overcome a certain resistance on the part of production workers, but now the work is being carried out very successfully through the joint efforts of the Institute and the factories, and major successes are already evident, promising still more attractive prospects. This process of the “introduction” of physics into production began on the initiative of A. F. and is developing with his direct participation; and in this, undoubtedly, lies A. F.’s greatest service to the national economy of the Soviet country.

A. F. Ioffe and the Leningrad Physico-Technical Institute he created are not only a center of attraction for physicists, but in a certain sense also a center of “repulsive” forces. It was precisely from within the walls of the Physico-Technical Institute that, from among A. F.’s pupils, there emerged a number of major physicists of the many other physico-technical institutes of our country. In Tomsk and Baku, in Sverdlovsk and Kharkov, in Dnepropetrovsk and Tbilisi, alumni of the Physico-Technical Institute are at work—pupils of A. F. or pupils of his pupils. Fortunately, these repulsive forces did not compensate the forces of attraction, and physicists working in different parts of our immense country do not lose their connection with the Leningrad Physico-Technical Institute and its director.

A. F. always stands at the center of all major physical events in the country. Practically not a single undertaking important for physics and physicists takes place without his direct or indirect participation. He notices the emergence of a new and important current at its very inception and quickly reacts to it, drawing into its development all living creative forces. With extraordinary foresight he anticipates the course of events and mobilizes forces in good time for the solution of the tasks ahead.

In 1918–1919, through the smoke of the blazing fire of the Civil War, A. F. sees the outlines of future socialist technology and sets about organizing scientific work in physics—the foundation of this technology. Foreseeing the need for corresponding cadres of physicists, he at once organizes a physico-mechanical faculty at the Polytechnic Institute. In the years of the Stalin five-year plans, A. F. broadens the front of work in technical physics to aid rapidly growing industry.

In 1932–1933, A. F., together with the foremost physicists of the world, senses the necessity of developing a new field of atomic physics—nuclear physics—which until then had scarcely been cultivated in the country. As a result of bringing the best forces to bear on this question, the Physico-Technical Institute, in a short period, was able in this field as well to enrich science with a number of major works carried out within its walls.

This remarkable ability to sense the new and the important is the most characteristic trait of A. F., one that has ensured him exceptional success in his work and has won him exceptional authority and popularity.

A. F. Ioffe began his scientific activity after graduating from the Petersburg Technological Institute, in the laboratory of one of the best experimenters of that time—W. K. Röntgen, in Munich.

The first work that he undertook at Röntgen’s suggestion was an investigation of the cause of the electrification of quartz under deformation. The method for studying this phenomenon was based on the study of elastic aftereffect. A. F. Ioffe, however, showed from the very beginning that the elastic aftereffect itself is a secondary phenomenon, caused by the fine-crystalline structure and by the appearance of electric charges inside the specimen when it is deformed. Having eliminated the possibility of charge formation (by illuminating the specimen with short-wave light), A. F. succeeded in eliminating the aftereffect itself as well. Thus the elastic aftereffect, which was supposed to serve as the means of investigation, was turned by A. F. into the object of investigation. This first major scientific work of A. F. gives an idea of the distinguishing traits and special features of all his subsequent scientific work. In choosing a method of scientific investigation A. F. followed his own path, in contrast to the methodology of his famous teacher.

Röntgen, according to A. F. himself, tried in his work to study one fact or another with maximum objectivity, avoiding the expression of any hypotheses about its cause and not attempting to explain it. A. F. Ioffe, on the contrary, tried to set up and explain every experiment against the background of those conceptions that he developed about a given phenomenon.

Thus, at the beginning of his work on the study of elastic aftereffect, A. F. developed for himself a general conception of the structure of crystals, from the standpoint of which there should be no elastic aftereffect in a perfect crystal, and all subsequent experiments were subordinated to this general idea. This unquestionably correct method of scientific investigation—when experimental work must be preceded by a more or less clearly formulated conception of the expected result on the basis of one or another theoretical picture—A. F. Ioffe later taught to his numerous students as well.

In 1906 A. F. Ioffe returned to Petersburg. Having declined the professorship offered to him in Munich, A. F. was enrolled as a laboratory assistant in physics at the Polytechnic Institute. Soon a group of physicists gathered around him to solve the problems he posed.

A. F. succeeded in introducing a new current not only into scientific work but also into the teaching of physics. Instead of the usual routine method of presenting a physics course, in which for half a year the listeners were taught methods for measuring length, angles, weight, etc., A. F. began the course with general ideas about the structure of the atom, molecular forces, and crystal lattices. Thus the foundation was laid for a new approach to the teaching of physics in higher education, which, with minor changes, has survived to this day.

Scientific work proceeded, on the one hand, in the direction of studying the electrical properties of crystals, and, on the other hand, in investigating the nature of light and the atomic structure of electricity.

A. F. always was, and remains, at the center of “physical events,” taking up and posing the physical problems most topical at a given moment, and at times turning one problem or another into one of the most urgent in physics.

It is therefore not surprising that, at the dawn of the development of atomistic views on electricity and light, these questions were at the center of his attention.

The nature of light, according to A. F.’s own testimony, interested him already from his school days. At the end of 1905 Einstein’s work on light quanta appeared. A. F. immediately began to set up experiments to test the theory. To this end he carefully analyzed Ladenburg’s experiments and showed, contrary to the assertions of Ladenburg himself, that they agreed with Einstein’s theory. As is known, Millikan preceded A. F. in publishing the results of the verification of Einstein’s theory.

Later A. F. again returned to the study of the nature of light. His now classic investigations of the elementary photoelectric effect, his widely known experiments on the photoeffect with microscopic bismuth dust, provided the most immediate and direct proof of the quantum nature of light.

At that time (the 1910s), alongside his work on the theory of light, A. F. devoted great attention to the experimental substantiation of the atomic structure of electricity. As is known, the attempts of numerous investigators to detect a magnetic field around a cathode beam had not been crowned with success. A. F. Ioffe, in experiments brilliant in ingenuity and precision, detected and measured the magnetic field created by cathode rays.

Further, the well-known experiments with the elementary photoelectric effect from metallic particles in an Ehrenhaft condenser (which Millikan also used) gave convincing proof of the reality of the electron.

Thus the establishment of the most fundamental facts of modern physics was carried out with the very active participation of our scientists in the person of A. F. Ioffe. It is clear that the works listed placed A. F. Ioffe among the ranks of the greatest physicists in the world.

Outwardly, this fact was marked by the election of A. F. in 1920 as a full member of the Academy of Sciences; at the present time A. F. Ioffe is a member of five academies of sciences of the world and of a number of scientific societies.

A particularly wide scope was attained by A. F.’s scientific work after the Revolution.

From the very first days of the establishment of Soviet power, A. F. set about organizing the Physico-Technical Institute in Leningrad—the nucleus of the future development of physics in the country. Here the principal cadres of Soviet physicists grew up; here, for the first time, the scientific work of physicists was placed on a new foundation, which was to become the scientific foundation of socialist technology.

The main core of the new physics center was formed by A. F. Ioffe’s closest pupils and collaborators from his work at the Polytechnic Institute. These were N. N. Semenov, Ya. I. Frenkel, P. L. Kapitsa, N. I. Dobronravov, Ya. G. Dorfman, and others.

A number of physicists from Leningrad and Moscow joined this group.

At the Physico-Technical Institute, A. F. was able to create a special scientific atmosphere. It is difficult to formulate precisely what characterizes this scientific atmosphere. Apparently, it is determined by a whole series of small features, at first glance, the combination of which creates an exceptional environment conducive to fruitful, intensive scientific work. Most physicists directly feel the special nature of the scientific environment prevailing at the Physico-Technical Institute.

This is promoted to a considerable degree by the fact that A. F. always paid exceptional attention to raising the scientific qualifications of his collaborators, persistently demanding that every staff member be fully abreast of modern physics, follow the literature, actively participate in the scientific seminars that have existed in the Institute from its very foundation, etc.

The Physico-Technical Institute, invariably directed by A. F. Ioffe to this day, has become the most important center for the development of physics in the country. From its personnel were drawn cadres for a number of other physico-technical institutes of the USSR, which were organized on the initiative and under the direct leadership of A. F. Thus, institutes were created in Kharkov, Dnepropetrovsk, Tomsk, and Sverdlovsk.

Having set himself the goal of organizing scientific work in physics in a new way, so that it would exert a fruitful influence on the future technology of the Soviet country, A. F. also provided for the creation of the necessary source of cadres of Soviet physicists familiar with technology.

As has already been indicated, in 1919 the Physico-Mechanical (now Engineering-Physics) Faculty was organized at the Polytechnic Institute; its twentieth anniversary was celebrated by physicists last year. For ten years A. F. was dean of this faculty and directly directed the establishment of its educational work and its organization.

It is difficult in a short article to enumerate the whole complex of organizational measures that were carried out by A. F. in order to achieve the principal goal he had set and that was supported in every way by the Soviet government—the creation of a physical scientific base for socialist technology.

Along with the organization of the Physico-Technical Institute and the Physico-Mechanical Faculty, the Leningrad Physico-Technical Laboratory was organized; a plan was drawn up for equipping hundreds of factory laboratories, which was largely carried out.

In 1918 A. F. returned again to the problem of the mechanical properties of matter, in particular, to elucidating the mechanism of plastic deformation. The first result of these studies was, now

a fact familiar to everyone from textbooks: the appearance of asterism on Lauegrams taken from a deformed crystal. It was possible, as it then seemed, to establish the minimum stress necessary for the onset of plastic deformation (slips). But soon more sensitive optical methods, applied to detect slips, substantially lowered the elastic limit for crystals (down to \(10\ \mathrm{g/mm^2}\) for rock salt). A connection was also established between the number of slips and the hardening of the deformed crystal.

A. F. never was, and is not, satisfied with solving particular questions and problems of one or another area of physics, striving whenever possible to encompass more broadly, by his investigations, the area that interested him. In studying the mechanical properties of matter, A. F. likewise could not confine himself to investigating only the mechanism of plasticity, but extended his research also to the fundamental problem of the mechanical properties of matter—its strength.

The theory of the crystalline lattice developed by that time by Born was in obvious contradiction with the experimental data on the strength of crystals. Experiment gave a significantly lower strength than the theory required.

A. F. set himself the goal of resolving this contradiction. There followed a whole series of brilliant experiments by A. F. with a number of his collaborators; although these experiments did not completely solve the problem posed, they did lead to the discovery of major facts. It was shown that the tensile strength of a crystal depends substantially on the condition of its surface. Without entering into a detailed analysis of all this enormous work, one should point to one of its classic results, which has now received the name of the Ioffe effect—an effect whereby a specimen in which the possibility of formation of surface cracks has been eliminated (rock salt in water) acquires increased strength. This effect has now already become the subject of lecture demonstrations in physics.

Within the walls of the Physico-Technical Institute, A. F. continued his work on the study of the electrical properties of dielectric crystals. This field, in which A. F. and his school obtained an exceptionally large number of results, was developed with particular intensity up to 1934–1935. One of the most essential results, obtained already in the earliest experiments on the investigation of the electrical conductivity of crystals, was the establishment of the role of dielectric polarization during the passage of electric current. Ohm’s law for dielectrics was “saved,” i.e., the independence of the resistance of a dielectric from the potential difference was established. A. F. took into account that the potential difference under which the specimen is placed is not equal to the applied emf, but is reduced by the magnitude of the polarization potential difference. There then followed a large series of works by A. F. and his collaborators on the investigation of the temperature dependence of the electrical conductivity of crystals, the influence of impurities, and so on. A whole series of exceptionally ingenious methods of investigation was developed.

A. F. and his school had to withstand an extensive polemic with the school of the German physicist Smekal on the question of the mechanism

electrical conductivity of crystals and the role of inhomogeneities in them. Extensive studies undertaken in this connection fully confirmed the correctness of Ioffe’s school, as was beyond doubt established during the discussion held in Berlin in 1930.

It is noteworthy that, although the picture of dielectric breakdown that emerged in the course of the experimental studies later proved to be erroneous (owing to inaccuracies admitted in the interpretation of certain measurement results), nevertheless these works yielded substantial technical results. On the one hand, new insulating materials (polystyrene and cellulose ethers) were created and studied, presenting significant advantages for the electrical industry. On the other hand, an entire independent technical branch of dielectric physics developed and grew, which is now already closely connected with industry.

Alongside these works, which were carried out personally by A. F. with his closest collaborators, a whole series of other directions in physics and technical physics developed at the Physico-Technical Institute under the leadership of A. F. A mere list of those new directions that were created and developed at the Physico-Technical Institute, and then in the institutes that separated from it, would take up an entire page. From this alone one can judge the scale of the scientific and scientific-technical work unfolded under the leadership of A. F.

In the years of the Stalin five-year plans, work in the field of technical physics, called upon to render direct assistance to our rapidly developing industry, expanded with particular intensity. Major scientific and technical forces were drawn into work at the Physico-Technical Institute. By the same time, numerous pupils of A. F. had grown into major scientists with world-renowned names (Academician N. N. Semenov, Corresponding Member of the Academy of Sciences Ya. I. Frenkel, Corresponding Member of the Academy of Sciences A. I. Alikhanov, Academician A. I. Leipunsky, Academician G. V. Kurdyumov, and others). The work of the physico-technical institutes created by A. F. began to exert a serious influence on our industry. New problems appeared, formulated by technology itself, which were successfully solved and are now being solved by a very large collective of qualified physicists.

One of such problems, on whose resolution A. F. has personally been working directly in recent years, was the problem of semiconductors. Semiconductors have recently found significant application in a number of branches of industry, chiefly in the form of photocells and rectifiers. The mechanism of action of both these and others was completely unclear. A. F., with a group of his collaborators, is closely setting about solving this problem.

From the theoretical point of view, this class of substances interests him as occupying an intermediate position between dielectrics and metals, so that the work on the study of semiconductors is a development of the work that was carried out at the Institute on the study of the electrical properties of dielectrics and metals. Having accepted-

took up this problem, A. F. set himself the goal of bringing the research to such a state that the technical problems of this field could be solved on the basis of a developed scientific theory. To a significant degree this goal has by now been achieved.

The first two or three years were devoted to the theoretical and experimental study of the electrical and photoelectric properties of semiconductors. The phenomena at the metal–semiconductor boundary were studied in detail (rectification). On the basis of the richest experimental material, first a general scheme of the phenomenon of rectification and of the blocking-layer photoeffect was developed, and then the theory of these phenomena. After this A. F. and his collaborators could already, if one may put it so, “design” the required photocell and rectifier and consciously alter their characteristics.

At present the rectifiers developed in A. F.’s laboratory are being manufactured at factories and, in quality, in any case are not inferior to foreign ones. The photocells developed in his laboratory are the most sensitive in the world and are already finding broad application in a number of branches of technology.

The Physico-Technical Institute headed by A. F. is at present one of the foremost scientific institutions of the USSR. Its work in the field of nuclear physics, in the field of studying the properties of liquids and amorphous bodies, and in the field of the electrical properties of matter has already yielded a number of outstanding results for science and for the national economy.

We wish A. F. Ioffe equally fruitful work in the future for the benefit of the science and technology of our socialist motherland.