**Sveatoslav MOSKALENKO**

### (1928 – 2022)

Sveatoslav Moskalenko (Moscalenco), Academician of the Academy of Sciences of the Republic of Moldova (ASM), Professor, Dr. hab.., Head of a department of the Institute of Applied Physics (IAP) was born on September 26, 1928 in the village of Bravicea village of Bravicea, Calarasi district, the, Republic of Moldova. Sveatoslav Moscalenco joined the Academy of Sciences of the Republic of Moldova in 1960 after graduating from the Institute of Physics of the Academy of Sciences of Ukraine, Kiev, and obtaining his PhD degree in physical-mathematical sciences. From 1964, the year of the foundation of the Institute of Applied Physics, until 2022 he was the Head of the Section of semiconductor theory and quantum electronics (now Theoretical Physics Laboratory “Vsevolod Moscalenco”). He obtained his Dr. hab. degree in 1970 at the Joint Scientific Council of four Institutes in Kiev. He was awarded the title of Professor in 1974. He was elected Corresponding Member of the ASM (1989) and Full Member of the ASM (1992). Academician Moskalenko was the scientific adviser of 25 Ph.D. and 5 Dr. hab. (post-doc) students of his section/laboratory at the IAP. | |

Awards: the State Prize of the Moldavian SSR (1981) and the State Prize of the USSR in the field of Science and Technology (1988),
Decorations: The Order of Glory of Labour (1971), The Order of the Republic (1996), “Dimitrie Cantemir” Medal of the Presidium of the ASM (1998), ASM Medals “Scientific Merit” of the 2nd degree (2016) and of the 1st degree (2018). Honorary titles: Honored Citizen (2001); Honorary countryman of his native village Bravicea (2003). Academician Moskalenko was the author of five monographs including one published by the Cambridge University Press in 2000, co-authored with Professor David Snoke from the University of Pittsburgh, USA. He was also the author/coauthor of more than 800 scientific papers. Remarkable scientific results: Academician Moskalenko contributed to the foundation and development of the scientific basis of high-density exciton and biexciton physics in semiconductors, such as the concept of exciton molecule, called biexciton, consisting of four particles, two electrons and two holes, all four bound together by Coulombic forces, as well as a possibility of the formation of the Bose-Einstein condensate of excitons, i.e. quasi-particles with a limited lifetime, which are in a quasi-equilibrium state, the one far from a thermodynamic equilibrium, when the relaxation time is considerably shorter than the lifetime of the particles involved in the process. He predicted superfluidity of excitons and biexcitons – a phenomenon that would clearly highlight a new phase. Those predictions, dating back to the years 1957-1959, stimulated experimental research in the respective directions, resulting in the experimental discovery of biexcitons in 1968 – first in CuCl and CuBr crystals and then even in Ge and Si crystals subjected to uniaxial deformation, where under low temperature conditions and at high degree of excitation, the formation of a metallic liquid composed of electrons and vacancies was observed. More recently, a spontaneous Bose-Einstein condensation (BEC) has been experimentally identified with certainty for excitonic polaritons in microcavities. Another prediction made, and then experimentally confirmed, was the induced formation of Bose-Einstein condensates of excitons, arising due to single-photon transitions under the action of resonant coherent laser light. For the case when coherent light is non-resonant, the virtual Bose-Einstein condensation of excitons was predicted. Later, induced Bose-Einstein condensation of biexcitons or even excitons due to resonant biphotonic transitions was also experimentally confirmed. The energy spectrum of cavity magnetic exciton polaritons which arise from the interaction of cavity photons with two dipole-active and two quadrupole-active branches of two-dimensional magnetic excitons excited on the surface of the GaAs quantum hole framed in the microcavity and subjected to the action of strong magnetic and electric fields perpendicular to the layer surface, was deduced. Landau quantization is assumed to occur at the lowest levels in the presence of the Rashba spin-orbital interaction in the case of electrons with a simple spin structure and heavy holes with the third-order chirality and dispersion law non-parabolicity. Academician Moskalenko also studied a possibility of the formation of molecular states of two-dimensional magnetic excitons. It was found that stable bound states do not exist. Instead it was established that a metastable state with a considerable activation potential, comparable to two ionization potentials of the magnetic exciton, does exist. The metastable state, following a radiative recombination of an electron-hole pair, gives rise to a new luminescence line with frequencies higher than the magnetic exciton luminescence line. He also established that under the influence of the Coulombic electron-hole exchange interaction, new states of one symmetric and one asymmetric superposition formed by two-dimensional (2D) magnetic excitons arise, whose electronic structure is determined by the Lorentz force and the direct Coulombic electron-hole interaction and is characterized by the sum spin projections of the electron-hole pair equal to F=±1. The symmetric state has a linear Dirac cone scattering law in the region of small wave vectors, while the asymmetric state has the same quadratic scattering law as the initial states of magnetic excitons. The statistical thermodynamics of the 2D Bose ideal gas with the linear dispersion law was developed. It was found that the second-degree phase transition occurs with the non-zero Bose-Einstein condensation critical temperature and heat capacity, which at the critical temperature is uninterrupted, without jump, as in the case of a 3D ideal Bose gas with the quadratic dispersion law. All these processes have been studied theoretically in the section and laboratory led by Academician Sveatosdlav Moskalenko. This contributed to the formation of new scientific directions and collectives, many of which branched out into research directions led by researchers who made their own names in theoretical physics. Among such directions may be mentioned the theory of nonlinear coherent propagation of light in the excitonic region of the spectrum in semiconductor and dielectric materials, which includes the theory of polariton solitons, the phenomena of optical bistability, self-reflection and others, known thanks to the contributions of university Professors Pyotr Hadji, Igor Beloussov, Anatol Rotaru, Anna Bobrysheva, Drs Igor Podlesny, Evgenii Dumanov, Elena Kiseleova and others. |