LABORATORY
COOPERATIVE PHENOMENA IN CONDENSED MATTER

HEAD: Prof. Dimo Uzunov, PhD, Dr.Sci.
tel: 7144-738; e-mail: uzun@issp.bas.bg

TOTAL STAFF: 5
RESEARCH SCIENTISTS: 2
Dr. D.V. Shopova, research fellow of I rank
PhD students: мag. V.G. Ivanov, мag. S.S. Savova
Physicist: мag. T.E. Tsvetkov
Free PhD course: mag. T.P. Todorov (TU-Sofia)

RESEARCH ACTIVITIES:

    A theoretical prediction for a stable non-collinear phase in complex two-sub-lattice antiferromagnets has been made [1].
    Several basic problems of the theory of quantum phase transitions have been reviewed. The effect of the quantum correlations on the phase transition properties has been considered with the help of basic models of statistical physics. Some new ideas and results have been presented. Outstanding theoretical problems have been outlined [2].
    A systematic treatment of the magnetic fluctuations effect on the properties of the normal-to-superconducting phase transition in a zero external magnetic field is given within the self-consistent approximation. The order parameter jump, latent heat, and specific heat are considered and numerically evaluated for bulk Al and thin Al films; as well as for W and In. The possibility for an experimental observation of the fluctuation change of the order of superconducting phase transition in superconducting films is discussed. The dimensional crossover in such films is also investigated [3-6].
    The phase of coexistence of superconductivity and ferromagnetism and the possible phase transitions of first and second order in spin-triplet ferromagnetic superconductors (UGe2, ZrZn2, URhGe) were investigated [7-9].

1. D. V. Shopova and T. L. Boyadjiev, Phys. Lett. A 311 (2003) 438, The existence of a stable noncollinear phase in Heisenberg model with complex structure.
2. D. V. Shopova and D. I. Uzunov, Phys. Rep. C 379 (2003) 1-67, Some basic aspects of quantum phase transitions.
3. D. V. Shopova, T. P. Todorov, and D. I. Uzunov, Mod. Phys. Lett. B 17 (2003) 141, Thermodynamic properties of the phase transition to superconducting state in thin films of type I superconductors.
4. D. V. Shopova and D. I. Uzunov, Phys. Lett. A 313 (2003) 139, Phase diagram of a class of spin-triplet ferromagnetic superconductors.
5. D. V. Shopova, T. P. Todorov, Phys. Lett. A 314 (2003) 250, Dimensional crossover of the thermodynamic properties near the phase transition in type I superconductors.
6. D. V. Shopova, T. P. Todorov, J. Phys. Condensed Matter, 15 (2003) 5783, New features of the phase transition to superconducting state in thin films.
7. D. V. Shopova, T. P. Todorov, J. Phys. Studies 7 (3) (2003), Novel results about the magnetic fluctuation effects near the normal-to-superconducting phase transition.
8. D. V. Shopova, D. I. Uzunov, J.Phys. Studies 7 (4) (2003), Homogeneous phase coexistence of spin-triplet superconductivity and ferromagnetism.
9. D. V. Shopova, D. I. Uzunov, Compt. Rend. Acad. Bulg. Sci. 56, 35 (2003), Thermodynamic properties of the phase transitions in a class of spin-triplet ferromagnetic superconductors.

1. Statistical theory of phases and phase transitions in superconductors and magnetic systems at low temperatures ( BAS).
2. Theory of Superconductivity (Scenet-2: Programme of EC - 6th FP).
3. Magnetic effects in unconventional superconductors (Contract 10/98-2003 - JINR).

1. Current CPCM Laboratory regular seminars, in total: 7 hours.
2. A lecture course of 32 hours on Physics of Phase Transitions for PhD students of BAS.
3. A Seminar given in MPI - PKS - Dresden: ``The non-universality of the quantum critical behaviour of ordered and disordered Bose fluids."
4. Three ISSP Seminars, and a lecture (Colloquium of The Inst. of Physical Chemistry - BAS) have been given.
5. A lecture has been given at a Seminar for post-graduates (Vitosha, BAS, 2003).

    In 2003 three post-graduate students worked in the Lab. A fourth PhD student was accepted in the end of 2003; effective from the beginning of 2004. Two visits of International Schools (Corsica and Cambridge) and a three month specialization in Cambridge have been ensured for two post-graduate students of ISSP-BAS.

    A PhD thesis was defended in Dec 03 (T. P. Todorov). A PhD thesis passed the preliminary defense (I. P. Takov).

1. The head of the Lab has been active also as a Member of the Editorial Board of J. Phys. Studies (Ukraine), Ref. Board of The Institute of Physics (London), and the Board of Advisors of ABI (USA).
2. A collaborative visit (56 days) in MPI-PKS (Dresden) has been performed.
3. The activity in the European Network of Superconductivity (SCENET) has been carried out according to the existing schedule. The Laboratory was established as a National leader in the European Superconductivity Network (SCENET) - 6th FP (2003-2007), and the first Bulgarian scientific unit included in the 6th FP of the EC.

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