Department for Theory of Model Spin Systems

The Department was founded in 1995. Professor Roman Levitsky was the Head of the Department up till 2003. Since 2003 Derzhko Oleh, PhD is the Head of the Department. The staff of the Department always ranged from 10 to 12 people. Since foundation of the Department the number of staff members with scientific degree has been constantly increasing and the following members obtained a PhD degree: Sokolovsky R., Moina A., Verkholyak T., Baran O., Zaburany O., Lisnii B., Vdovych A. while Derzhko O. defended a postdoctoral thesis). Today the Department employs 2 Professors, (Levitsky R.R., Derzhko O.), 7 PhDs (Sorokov S., Shchur Ya., Baran O., Sokolovsky R., Moina A., Lisnii B., Vdovych A.), as well as young researchers and PhD students (Andrusyk A., Maksymenko M., Topilko M.).

Basic scientific fields

• Theory of the order-disorder type ferroelectrics specifically with hydrogen bonds; phase transitions and dielectric properties; external fields effect
• Modeling of the lattice dynamics of the complex ferroelectric crystals
• Development of the analytic and numerical methods in theory of classic and quantum spin models; accounting of the different types of interactions and accounting of the disorder; theory of the spin (proton) glass; applying to the theory of the ferroelectrics
• Theory of the low dimensional quantum spin models
• Theory of the quantum spin models with frustrations
• Theory of the liquid-crystalline systems: analytic and numerical methods

Scientific cooperation

The members of the Department are involved into joint scientific researches with the researchers of other scientific institutions in Ukraine and abroad, in particular, they work with researchers of Lviv Ivan Franko National University (Ukraine), Lvivska Politekhnika National University (Ukraine), Uzhhorod National University (Ukraine), Magdeburg University (Germany), Dortmund University (Germany), University of British Columbia (Vancouver, Canada).

Lecturing

Derzhko Oleh did lecturing at the Condensed Matter Physics Department and Theoretical Physics Department of Lviv Ivan Franko National University and at Lvivska Politekhnika National University. Postgraduate student studied at the Department (supervisors - Levytsky R.R., Derzhko O.).

Some recent publications

1. R.R.Levitskii, B.M.Lisnii. Theory of related to shear strain u6 physical properties of ferroelectrics and antiferroelectrics of the KH2PO4 family // Physica status solidi (b) 241 (2004) 1350.
2. T.G.Sokolovska, R.O.Sokolovskii, G.N.Patey. Surface-induced ordering of nematics in an external field: The strong influence of tilted walls // Phys. Rev. Lett. 92 (2004) 185508.
3. J.Richter, O.Derzhko, J.Schulenburg. Magnetic-field induced spin-Peierls instability in strongly frustrated quantum spin lattices // Phys. Rev. Lett. 93 (2004) 107206.
4. A.P.Moina, R.R.Levitskii, I.R.Zachek. Piezoelectric resonance and sound attenuation in the Rochelle salt NaKC4H4O6·4H2O // Phys. Rev. B 71 (2005) 134108.
5. O.Derzhko, T.Krokhmalskii, J.Stolze, G.Müller. Dimer and trimer fluctuations in the s=1/2 transverse XX chain // Phys. Rev. B 71 (2005) 104432.
6. Ya.Shchur. Lattice dynamics study and specific heat of CsH2PO4 and CsD2PO4 // Phys. Rev. B 74 (2006) 054301.
7. R.R.Levitskii, O.R.Baran, B.M.Lisnii. Phase diagrams of spin-1 Ising model with bilinear and quadrupolar interactions under magnetic field. Two-particle cluster approximation // Eur. Phys. J. B 50 (2006) 439.
8. O.Derzhko, J.Richter. Universal low-temperature behavior of frustrated quantum antiferromagnets in the vicinity of the saturation field // Eur. Phys. J. B 52 (2006) 23.
9. T.G.Sokolovska, R.O.Sokolovskii, G.N.Patey. Colloidal interactions in nematic fluids // Phys. Rev. E 73 (2006) 020701(R).
10. O.Derzhko, A.Honecker, J.Richter. Low-temperature thermodynamics for a flat-band ferromagnet: Rigorous versus numerical results // Phys. Rev. B 76 (2007) 144418.