Department of Physics, Tel: +44 (0) 1509 22 8409

Bakhrom Yavidov

 

 

Dr Bakhrom Yavidov

NATO/Royal Society Postdoctoral Fellow

Quantum Structures and Phase Transitions group

My field of interest is polaron formation in solids: the definition, energy and mass of a polaron and the pairing of polarons to form a quasiparticle — the bipolaron — proposed as a more relevant charge carrier in high-temperature superconductors.  High-temperature superconductors are complex solids akin to doped semiconductors: many of their features depend on the impurity or defect concentration.

That is why the topic of my Ph.D. thesis was "The theoretical investigation of formation of impurity bipolarons in covalent semiconductors and high-temperature superconductors", which I defended on 31 January 2002. Impurity bipolarons are the same as Anderson's negative-U centres that occur when Hubbard on-site (impurity or defect) repulsion energy between charge carriers is negative due to interaction of the carriers with the deformation of the surrounding medium. This deformation falls off at large distances in the usual molecular crystal model and this case corresponds to local deformation. The usual continuum study of polaron formation envisions deformation as large and irrelevant at small distances compared to lattice constant. In real situation we have both "small-size" and "large-size" deformations due to short- and long- range interactions, respectively.

In my Ph.D. thesis I studied impurity (bi)polaron formation using Toyozawa's continuum approach, which takes into account both short- and long-range electron-lattice and electron-impurity interactions. The stability region has been determined with respect to crystal parameters, and the energy of an impurity polaron and the binding energy of an impurity bipolaron have been calculated in the case of direct Coulomb correlation between carriers. The influence of lattice and impurity parameters on the formation and stability of impurity (bi)polarons is studied. The predictions of the model are applied to explain some experimental observations such as the decreasing of TC in doped HTSC's.

I am currently working in collaboration with Prof A S Alexandrov in the Quantum Structures and Phase Transitions group on the problem of polaron mass within the framework of a discrete lattice with long-range deformation.   

Publications:

  1. A.S.Alexandrov and B.Ya.Yavidov. Small adiabatic polaron with a long-range electron-phonon interaction. Phys. Rev. B, 69, 073101 (2004).
  2. B.Ya.Yavidov. Optical conductivity of small adiabatic polarons with a long-range electron-phonon interaction. quant-ph/0401089.
  3. S. Dzhumanov, U. Begimqulov, U. T. Kurbanov and B. Y. Yavidov. On the Mott transition and the new metal-insulator transition in doped covalent and polar crystals// Preprint ICTP, Trieste, IC/2001/139
  4. S. Dzhumanov, U. Kurbanov, A. Kurmantayev, B. Yavidov. Distinctive Mott transitions in doped covalent and polar crystals//Abstracts of 4th Int. Conf. "Modern problems of Nuclear Physics", Tashkent (O'zbekistan), 2001, p.158
  5. S. Dzhumanov, A. Baratov, B. Yavidov. Formation of large and nearly small strong-coupling bipolarons and their relevance to high-TC superconductivity//Abstracts of 6th Int. Conf. on materials and mechanisms of superconductivity high-temperature superconductors, Houston (Texas, USA) 2000, 4PO8-57
  6. S. Dzhumanov, U. Begimqulov, A. Kurmantayev, U. Kurbanov, B. Yavidov, R. Yusupov. Formation of one-carrier and two-carrier impurity states and bands in doped insulators and semiconductors//Vestnik KGNU named after Al-Farabiy, 2(9) 2000, p.43-47
  7. S. Dzhumanov, U. Begimqulov, A. Kurmantayev, U. Kurbanov, B. Yavidov, R. Yusupov. Formation of one-carrier and two-carrier impurity states and bands in doped insulators and semiconductors//Abstracts of 6th Kazakhstan Conference on Solid State Physics, Aktobe (Kazakhstan), 2000, p.9-11
  8. S. Dzhumanov, A. A. Baratov, U. Kurbanov, T. I. Umaraliev, B. Yavidov. The continuum theory of nearly large and small multi-site bipolarons in weakly doped high Ð TC superconductors//Abstracts The 3rd Int. Conf. "Modern problems of Nuclear Physics", Bukhara (O'zbekistan), 1999, p.347
  9. S. Dzhumanov, B. Yavidov, N. A. Makhkamov. Negative U Ð centres and defect superconductivity //Superlattices & Microstructures, v.21, no.3, 1997, p.325-327   
  10. M. C. Yunusov, S. Dzhumanov, B. L. Oksendgendler, A. Axmadaliyev, B. Yavidov. Continuum model of self-trapping of the carriers in the vicinity of a defect's and formation trapped states in covalent semiconductors. II. A possibility of application to d Ð impurities in n- and p-Si//O'zbek Journal of Physics, no. 1, 1996, p.29-33
  11. S. Dzhumanov, S. Kuchkarov, B. Yavidov. The formation of negative U Ð centres in solids//Abstracts of 9th Int. Conf. On radiation physics and chemistry of inorganic materials RXF-9, Tomsk (Russia), 1996, p.133-134
  12. S. Dzhumanov, B. Yavidov. Negative U Ð centres and defect superconductivity//Abstracts of 5th World Congress on superconductivity, Budapest (Hungary), 1996, p.220
  13. M. C. Yunusov, S. Dzhumanov, B. Yavidov. Continuum model of self-trapping of the carriers in the vicinity of a defect's and formation trapped states in covalent semiconductors. I. General theory//O'zbek Journal of Physics, no.6, 1995, p.21-26
  14. S. Dzhumanov, A. A. Baratov, B. Yavidov. Specific character of one-particle and two-particle self-trappings in the vicinity of defects crystalline//Abstracts of Republic Conference in honour of 600 anniversary of Muhammad Tarag'ay  Ulug'bek, Gulistan (O'zbekistan), 1994, p.105 
 
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