LABORATORY
ELECTRON-PHONON INTERACTIONS

HEAD: Kate Christova, Ph.D.
tel: 7144-640; e-mail: kkp@issp.bas.bg

TOTAL STAFF: 8
RESEARCH SCIENTISTS: 7
M. Georgiev, Ph.D., Dr.Sci.
O. Ivanov, Ph.D.
L. Mihailov, Ph.D.
A. Andreev, Ph.D.
Z. Dimitrova, Ph.D.
G. Kamisheva


RESEARCH ACTIVITIES:

  1. SYMMETRY LOWERING, VIBRONIC EFFECTS AND WAVES IN HIGH-TEMPERATURE SUPERCONDUCTORS AND OTHER CRYSTALS

    • VIBRONIC POLARONS

          A model is proposed which broadens the classical approach for the temperature dependence of the diffusion coefficient of C in Fe at low temperatures (below liquidN). The model regards the possibility of quantal horizontal tunneling and one-phonon processes to support the diffusion. The role of the letter falls as the temperature is risen. The one-phonon correction is also used in the study of the electric resistivity dependence ρ(T)in superconducting cuprates.

          The hopping energies of the Metal(P)-O(A) transition is calculated for superconducting cuprates and colossal magnetoresistance exhibiting manganates. On the basis of these calculations is made the conclusion that the current along the O(A)-M(P)-O(A) bond is due to strong coupled "bond" polarons.

          The Merrifield Variational Ansatz is extended so as to cover the Jahn-Teller and Pseudo Jahn-Teller polaron cases. Calculations for the translations of such polarons along linear chain are made for the low-energy region, for which is believed the adiabatic approximation not to work properly.

    • RELATIVISTIC CORRECTIONS AND EXTERNAL ELECTROMAGNETIC FIELD IN THE SPIN DENSITY MATRIX AND SPIN DENSITY FUNCTIONAL METHODS

          Using the DFT (Density functional theory) for many-electron systems it is proposed an integrated electron density matrix approach for the determination of nuclear multipole moments (with relativ-istic corrections) for all possible hyperfine interaction operators, including the yet unobserved magnetic octupole couplings. The matrix elements of the electron-nuclei multipole interaction operators obtained by using a perturbation approach of the Hamiltonian as a series of powers of the ratio of nuclear and electronic coordinates and by expanding the Hamiltonian as a series of powers of the fine structure constant, which involves the relativistic corrections, have the same analytical forms in all cases.

  2. SURFACE PHOTO-CHARGE EFFECTS (SPCE) AND ITS APPLICATION

        As a result of many experiments an substantial widening of the range of action of SPCE was established: the effect takes place out of the scale of visible light and close regions; the SPCE was observed also for frequencies up to 1 GHz. The development of devices on the base of this effect for contactless express chemical composition test of samples of different materials is possible. Such method allows, for example, identification of false coins.

  3. MECHANICAL STRESS IN CHALCOGENIDES

        Thermally evaporated films of GexSb40-xS60 were studied further by XPS and Atomic Force Microscopy (AFM). The analyses of XPS of fresh and treated (illuminated and/or annealed) films show the coordination number correction necessity, as well as the complicated Sb contribution to film peculiarity. The surface of fresh and double treated (x = 5) films was observed by AFM. It can be suggested through AFM images that the roughness scale changes like mechanical stress with the film composition variation.

  4. TIME SERIES ANALYSIS

        The behavior of system of population was investigated in the case of dependence of interaction coefficients of the number of members of populations . With WTTM method of analysis of multifractal properties of time series the correlation with long range in the system of three populations were investigated.

  5. DYNAMIC TRACTION FORCE INTEGRATOR (DTFI)

        A two-years project is finished and DTFI system is in regular operation of Sept. 2003. An original algorithm for fast route creation and modification is elaborated. The Integrator gives the opportunity to calculate the shortest route through given number of points. An optimization program for traction force characteristics desctription has been developed. The travelling time error is up to 50 sec within 500 km. All the traction force calculations for train schedule in Bulgaria are performed by the DTFI. DTFI maintains any changes in the current schedule and is working out schedule-projects with, making Bulgarian railways able to meet EU needs as well.

  6. HISTORY OF PHYSICS IN BULGARIA

        The study on the history of theoretical physics in Sofia University, the history of Institute of Solid State Physics and on some biographies of scientists (M. Borisov, A. Vavrek, J. Kasabov, P. Kamadgiev) are continued. In the case of both latter, posters of May 2003 are exposed at "the Earth and the People" Museum


PUBLICATIONS:
  1. K. Christova, A. Manov, V. Pamukchieva, A.G.Fitzgerald, L. Jiang "Mechanical stress studies of amorphous GexSb40-xS60 film" J. Non-Cryst. Solids 325, 1-3, 142 (2003).
  2. R. L. Pavlov, P. P. Raychev, V. P. Garistov, M. Dimitrova and J. Maruani "Nuclear moments and electron density matrices in atoms" Int. J. Quant. Chem. (2004), in press
  3. O. Ivanov "Charging of Solids on irradiation with an electromagnetic field" Optics Communications (2004), in press
  4. Z. Dimitrova, N. Vitanov "Chaotic pairwise competition" Theor.Popul.Biology (2004), in press
  5. L. Dabrowski, A. Andreev and M. Georgiev "Carbon diffusion in a-iron: evidence for quantum mechanical tunneling" Annual Report Institute of Atomic Energy, Swierk, Poland
  6. S. Tsintsarska, M.D. Ivanovich, M. Georgiev, Alexander D. Gochev "The 0-M-O triatomic molecule: basic unit of cuprates & manganates" Bulgrian Journal of Physics, 2003, in press
  7. S.G. Tsintsarska, M.D. Ivanovich, A. Andreev, D.W. Brown, K. Lindenberg, M. Georgiev "Itinerant vibronic polarons: A Merrifield approach 1. Low Energy range calculations" Bulgrian Journal of Physics, 2003, in press
  8. G. Kamisheva "History of the Mathematical and Theoretical Physics in the Sofia University (1925-1935)" Proceedings of the Fifth General Conference of the Balkan Physical Union, Vrnjacka Banja, Serbia and Montenegro, August 25-29, 2003, Eds. S. Jokic, I. Milosevic, A. Balaz, and Z. Nikolic, p. 1999-2002 - in CD (2003)
  9. Г. Камишева, А. Г. Петров "30 години институт по физика на твърдото тяло при БАН. Исторически корени и настояще" Списание на БАН, 1, 80-86 (2003)
  10. Г. Камишева "Историята на физическите науки в творчеството на акад. М. Борисов (18.02.1921-05.11.1998) Сборник в памет на академик Милко Борисов, ИФТТ
  11. Г. Камишева "ИФТТ "Акад. Г.Надж." на 30 години" Светът на физиката, 1, 58-60 (2003)
  12. Г. Камишева-In memoria ст.н.с.А.Ф.Ваврек (1947-2003) Светът на физиката, 4, 385 (2003)
  13. Г. Камишева "Сесия в памет на академик Милко Борисов" Светът на физиката.
  14. Г. Камишева "Музей на физическите науки в България" Светът на физиката.

ONGOING RESEARCH PROJECTS:
  1. Symmetry lowering, vibronic effects and waves in high-temperature superconductors and other crystals.
  2. Structure and dynamics of many-electron systems (COST D9/0010 P& M Curie Univ. Paris)
  3. Surface photo-charge effects (Jagellon Univ. Krakow, Poland)
  4. Mechanical stress in chalcogenide GeSbS film-Si substrate system
  5. Dynamic traction force integrator (Bulg. Railways)
  6. Extracting information from time series (Min. of education&science)
  7. Founders of science and higher education in physics in Bulgaria
  8. The role of Acad. G. Nadjakov in the history of physics in Bulgaria

Top

to CONTENTS