Obituary of Evgenii Moskalenko (1963-2012)

1986-1991 - doctoral student at the A.F. Ioffe Physico-Technical Institute (FTI) of the Russian Academy of Sciences, Sanct-Peresburg, Russia. 1991-2012 - Doctor of science, junior and senior collaborator of the FTI. 1999-2012 - invited researcher at the department of physics and measurement technology of the Linkoping University in Sweden.

In memoriam:

Doctor Evgenii S. Moskalenko

05.05.1963-12.03.2012

Evgenii Moskalenko, originally from Republic of Moldova was born in Chisinau in May 1963 and died unexpectedly due to heart embolism in March 2012 in Sanct-Petersburg, Russia being 49 years old. He graduated from the Chisinau secondary school in 1980 and the physical faculty of the St. Petersburg State University in 1986. He was a doctoral student of the A.F. Ioffe Physico-Technical Institute(PTI) in St. Petersburg of the Russian Academy of Sciences under the scientific guidance of the academician A.A. Kaplyanskii and in 1991 performed his doctoral thesis and obtained the candidatus scientiarum degree. His thesis was dedicated to the influence of the non-equilibrium acoustical phonons arising during the relaxation of the photo-created carriers on the photoluminescence of excitons in semiconductors Si and Cu2O. The exciton drag driven by the ballistic acoustical phonons was observed and the deficit of the low-frequency terahertz phonon in comparison with the Planck distribution function was revealed.

The following 20 years of his post-doctoral activity were connected with the Department of the Solid State Optics of PTI, where he became a senior scientific collaborator growing as an experimental physicist in the range of optical spectroscopy of the solid states. His scientific interests were concentrated in the physics of excitons in semiconductors at high level of excitations and low temperatures. In the first decade of this activity he was engaged together with another collaborators of the PTI and of the University in Nottingham in England in the experimental attempts to achieve the Bose-Einstein condensation (BEC) of the trapped indirect excitons (IXs) in the double quantum well (DQW) structures. A giant increase of the luminescence intensity (intensity shot) of a part of the spectral profile of the IX line in the GaAs/AlGaAs-type DQW under the influence of the external electric field, at low temperature and at threshold pumping laser power was observed. It was attributed to the BEC of high density IXs localized in the trap formed by the inhomogeneity of the layer thickness.

The efforts of many experimental groups in the world were concentrated many years in the direction related with DQWs, nevertheless this topic remains up till now as an open question. But one may remember that the experimental investigations in this field in the former USSR at the end of the 20-th century required from the researchers many outstanding qualities such as devotion to the science, personal self-denial and enthusiastic attitude as regards such marvellous phenomena as the coherent macroscopic states in solid state physics, superfluidity and superconductivity. Evgenii Moskalenko was one of the pioneers who took part in the assault of this impregnable but attractive fortress.

In the last 12 years Evgenii Moskalenko simultaneously with his activity in PTI took part as an invited researcher in the investigations of the optical properties of the semiconductor nanostructures organized by Professor P.O. Holtz in the Department of Physics and Measurement Technology of the Linkoping University in Sweden. The phenomena of the optical orientation and spin polarization of electrons and nuclei in quantum dots were revealed. It has been established, that even for the case of the neutral exciton a nonzero nuclear magnetic field is builded up in the InGaAs/InAs QDs, when the spin-polarized electrons and holes are photogenerated by the circularly polarized light on the surface of the wetting layer. The variant when the electrons and holes are separately captured by the QD is studied. In this case the conduction electron is situated some time alone without the hole inside the QD and it succeeded to polarize the spins of the surrounding nuclei through the hyperfine contact Fermi interaction creating the nuclear magnetic field known as Overhauser field. The hole, arriving with time delay inside the QD, does not contact with nuclei because its p-type wave function inside the valence band, but it interacts with the electron forming the exciton The exchange electron- hole interaction is equivalent to an effective magnetic field. The exciton does exist in the presence of two orthogonal each other magnetic fields carrying out the precession around the total magnetic field. As a result the emission line of the exciton in the QD is partially circularly polarized.

The wonderful property of the Overhauser field is its very long lifetime due to very small dephasing processes determined by the dipole-dipole interaction of the spins of the neighbour nuclei. It is equivalent to a vey low effective temperature of the nuclear spin subsystem comparable with the famous low temperatures reached during the BEC of atoms in the traps.

Evgenii Moskalenko is the author of 65 papers in the referred journals as well as of 62 conference articles.

Professor Per Olof Holtz has written the following comments in memory of Evgenii Moskalenko.

“It was beyond doubt that Evgenii became an important and valuable member of our group during these 12 years. First of all, he was indeed a brilliant physicist, who strongly contributed to our interpretation and improved understanding of the properties of the quantum dots. He forwarded his ideas and achieved results in a congenial way. Evgenii was a person with a great curiosity, who could work exceptionally hard and with purposefulness and great excitement to reach the goal. I did value his experience, strengths, capability as exhibited in his work throughout the years. He also made a significant contribution in the supervision of several PhD students. The impact made by Evgenii in the way he forwarded his extensive knowledge and experience to my students was invaluable and highly appreciated by the students.”