|Alexei L. Efros - Curriculum Vitae|
PROFESSIONAL SERVICE and RECOGNITIONS:
BOOKS and MONOGRAPHS:
MOST SIGNIFICANT RESULTS:
1. I think my most significant result, obtained in collaboration with Professor B. I. Shklovskii, is the prediction of the Coulomb gap in the density of states of localized electrons (Efros and Shklovskii 1975, Efros 1976). The first paper has now about 1,800 references. It had been very controversial in the late 70th. I had a long dispute with the late Professor N. F. Mott, who even published a controversial paper about it, but finally we understood each other and he even came to Switzerland to meet me, when I was “permitted” by the USSR authorities to go abroad for the first time in my life. Now this theory is well established and it is widely used for interpretations of the variable range hopping experiments (Efros-Shklovskii law) and tunneling experiments for both 2 and 3-dimensional systems with and without magnetic field. The theory is important from a conceptual point of view. It claims that in the system with localized electrons the Coulomb interaction is not screened, and it is the long- range part of the interaction which is responsible for the gap in the density of states. This statement has been recently checked by direct experiment by A. J. Dahm et al. on the GaAs heterostructure where the Coulomb interaction was artificially cut by a close metallic electrode. The idea of the Coulomb gap exists in the modern physics in some different versions. Prof. Shklovskii and I were awarded by the Landau prize of the Academy of Sciences of the USSR for this series of works.
2. Theory of a hopping conductivity (HC) based upon the percolation principles (1971). This theory, created in collaboration with B. I. Shklovskii, provides a regular basis for calculations of the HC as a function of temperature, magnetic field, density of impurities, strain and so on. To calculate the activation energy of the HC the theory of the impurity band has been derived for doped and compensated semiconductors. Numerous theoretical results obtained have caused a burst of experimental studies and findings. The idea of the percolation approach was put forward independently by Ambegaokar, Halperin, and Langer (1971) and by Mike Pollak (1972).
These results are summarized in the monograph by Shklovskii and Efros "Electronic properties of doped semiconductors" published in 1979 in Russian by “Nauka” and in 1984 in English by Springer-Verlag (total about 4,5000 references). Even now it is still a handbook for people working in this field.
3. The new theory of the HC stimulated a development of the percolation theory. This was a concept of the correlation radius in the percolation and the first determination of the critical exponent of the correlation radius using finite-size percolation. These were also the thresholds for some new problems of percolation which appear in the HC theory. Probably, the most famous paper of this domain is "Critical behavior of Conductivity and Dielectric Constant near the Metal-non-Metal Threshold" by Efros and Shklovskii (1976). This paper has about 630 references. In 1982 I published a book for students "Physics and Geometry of Disorder" which explains the main ideas of the percolation theory and their physical applications. This book has been translated from Russian into English, Spanish, and Estonian.
4. The first theoretical study of quantum dots has been presented in the paper "Interband absorption of light in a semiconductor sphere" by A. L. Efros and Al. L. Efros (1982). The story runs like this: In 1981 Dr. A. Ekimov came to me to discuss his experimental results on, as it is called now, colloidal nanocrystals or quantum dots that he managed to synthesize, probably, the first in the world. He required an explanation of a peculiar optical properties of the dots, very different from those of the bulk material. I understood that the dimensional quantization was the main reason of the phenomenon. I invited my younger brother Alexander to create a quantitative theory of absorption of light and the theory of grows and dispersion of the sizes of the particles. We had no idea at the time that both the experiment and the theory will become the first or at least one of the very first works in the field that is called now "Nanophysics and Nanotechnology". The first paper has now about 1,700 references. One year later similar results were obtained by the US physicist L. Brus.
In 2006 our papers were reprinted in the volume 182 of the SPIE Milestone Series. In May 26 of 2014 a special International Conference was held in Paris with the title "30 years of quantum dots”. The Website of the Conference says that these 30 years originate approximately from our papers. Both Dr. Ekimov and my brother were the keynote speakers of the Conference.
In October of 2013 my brother and I published our second common work about the properties of the newly created crystalline structure with quantum dots instead of atoms. This system promises to become very important for photovoltaic. We were the first to formulate the main theoretical principles of such an unusual weakly disordered system. Nevertheless some questions are still open, and that is what I would like to do in the nearest years.
MOST RECENT INVITED TALKS AT INTERNATIONAL CONFERENCES:
"Photo and Dark Conductivity in Ordered Array of Nanocrystals."
International Conference on "Nanostructures: Physics and Technology". Petersburg, Russia, June 2014.
International Conference On Metamaterials and Nanophysics. Cuba, May 2014
International Conference on Transport in Interacting Disordered Systems, Barcelona, Spain, September 2013.