Structure / Departments / Department for Quantum Statistics

# Department for Quantum Statistics

The Department was founded in March 1980. Professor Ivan Oleksandrovych Vakarchuk was the first head of the Department (April 1, 1980 — September 17, 1984). Since March 21, 1986 and till April 30, 2016 it was headed by Corresponding Member of the National Academy of Sciences of Ukraine, Professor Ihor Vasylovych Stasyuk. In April 2016 the Department of Quantum Statistics and the Department for Model Spin Systems Theory were unified and Doctor of Physical and Mathematical Sciences Oleg Volodymyrovych Derzhko became the head of the Department. Among the former members of the Department there are O.L.Ivankiv, Yu.V.Kozitski, I.M.Kopych, S.S.Kotsur, H.V.Ponedilok, Yu.K.Rudavskyi, O.Ya.Saban,V.M.Tkachuk and others. Meanwhile, there are 18 researchers at the Department. Namely, 6 Doctors of Sciences: R.R.Levytskii, O.V.Derzhko, A.M.Shvaika, Ya.Y.Shchur, O.V.Velychko, A.S.Vdovych, 10 Candidates of Sciences: T.Ye.Krokhmalskii, R.Ya.Stetsiv, A.P.Moina, B.M.Lisnyi, O.R.Baran, O.P.Matveyev, G.O.Skorobagatko, O.M.Krupnitska, V.O.Krasnov, V.Ya.Baliha, as well as Yu.I.Dublenych and D.A.Dobushovskyi. There is 1 Ph.D. student at the Department (T.I.Hutak).

Research area of the Department covers a wide range of topics of current condensed matter physics such as the theory of strongly correlated systems (Hubbard, Falicov-Kimball, Heisenberg models), the theory of ultracold gases and intercalated layered crystal structures (Bose-Fermi-Hubbard and Bose-Hubbard models), the studies of classical and quantum spin models, in particular in low dimensions and with frustration, the investigations of ferroelectric ordering and other properties of ferroelectrics including the ones of nanosize. To these ends, various methods of equilibrium and nonequilibrium statistical mechanics are used. For instance, the Green functions approach or exactly solvable models as well as numerical methods such as the electronic density functional method, exact diagonalizations, classical and quantum Monte Carlo etc. All studies are aimed on obtaining the experimentally observable quantities, in particular, magnetization and polarization, specific heat, conductivity and thermoelectric coefficients, susceptibilities, optical spectra and inelastic (Raman) light and x-ray scattering spectra, as well as on constructing phase diagrams for a wide range of models and compounds. The researchers of the Department combine original analytical and numerical methods in their studies on the theory of strong electron correlations, magnetic and ferroelectric systems. There is a long-standing scientific collaboration with research groups from Germany, USA, Slovakia, Poland, Brazil.

### The head of the department - Dr.Sci., Prof. Oleg Derzhko

Oleg Derzhko was born on August 19, 1960 in L’viv. He graduated from the Ivan Franko L’viv University in 1982, earned the Candidate of Physical and Mathematical Sciences degree in 1988 and the Doctor of Physical and Mathematical Sciences degree in 2004, became the Senior Researcher in 1998 and the Professor in 2019. Since 2003 he headed the Department for Model Spin Systems Theory and since 2016 - the Department for Quantum Statistics. Research interests lie in the area of condensed matter theory and statistical physics.

Phone: (032) 2761978; E-mail: derzhkoicmp.lviv.ua

Recent research publications

- T.P.Devereaux, A.M.Shvaika, K.Wu, K.Wohlfeld, C.J.Jia, Y.Wang, B.Moritz, L.Chaix, W.-S.Lee, Z.-X.Shen, G.Ghiringhelli, L.Braicovich, Directly characterizing the relative strength and momentum dependence of electron-phonon coupling using resonant inelastic x-ray scattering, Phys. Rev. X 6, 041019 (2016).
- V.Myhal, O.Derzhko, Wetting in the presence of the electric field: The classical density functional theory study for a model system, Physica A 474, 293 (2017).
- Y.I.Dublenych, Ground states of a system of classical spins on an anisotropic triangular lattice and the spin-liquid problem in NiGa2S4 and FeGa2S4 compounds, Phys. Rev. B 96, 140401 (2017).
- J.Richter, O.Krupnitska, V.Baliha, T.Krokhmalskii, O.Derzhko, Thermodynamic properties of Ba2CoSi2O6Cl2 in a strong magnetic field: Realization of flat-band physics in a highly frustrated quantum magnet, Phys. Rev. B 97, 024405 (2018).
- G.A.Skorobagatko, Theory of interaction-dependent instability in quantum detection by means of Luttinger liquid tunnel junction: A rigorous theorem, Phys. Rev. B 98, 045409 (2018).
- O.Baran, V.Ohanyan, T.Verkholyak, Spin-1/2 XY chain magnetoelectric: Effect of zigzag geometry, Phys. Rev. B 98, 064415 (2018).
- I.V.Stasyuk, V.O.Krasnov, Repulsion-attraction asymmetry in the Bose-Fermi-Hubbard model, Physica B 552, 96 (2019).
- Y.Chen, Y.Wang, C.Jia, B.Moritz, A.M.Shvaika, J.K.Freericks, T.P.Devereaux, Theory for time-resolved resonant inelastic x-ray scattering, Phys. Rev. B 99, 104306 (2019).
- O.V.Velychko, I.V.Stasyuk, Thermodynamics of quantum lattice system with local multi-well potentials: Dipole ordering and strain effects in modified Blume-Emery-Griffiths model, Phase Transitions 92, 420 (2019).
- A.S.Vdovych, I.R.Zachek, R.R.Levitskii, I.V.Stasyuk, Field-deformational effects in GPI ferroelectric materials, Phase Transitions 92, 430 (2019).
- D.Kasprowicz, T.Zhezhera, A.Lapinski, M.Chrunik, A.Majchrowski, A.V.Kityk, Ya.Shchur, Lattice dynamics of Bi3TeBO9 microcrystals: Micro-Raman/IR spectroscopic investigation and ab initio analysis, Journal of Alloys and Compounds 782, 488 (2019).
- O.P.Matveev, A.M.Shvaika, T.P.Devereaux, J.K.Freericks, Stroboscopic tests for thermalization of electrons in pump-probe experiments, Phys. Rev. Lett. 122, 247402 (2019).
- P.Müller, A.Lohmann, J.Richter, O.Derzhko, Thermodynamics of the pyrochlore-lattice quantum Heisenberg antiferromagnet, Phys. Rev. B 100, 024424 (2019).
- O.Derzhko, T.Hutak, T.Krokhmalskii, J.Schnack, J.Richter, Adapting Planck’s route to investigate the thermodynamics of the spin-half pyrochlore Heisenberg antiferromagnet, Phys. Rev. B 101, 174426 (2020).
- G.A.Skorobagatko, Self-equilibration theorem in quantum-point contacts of interacting electrons: Time-dependent quantum fluctuations of tunnel transport beyond the Levitov-Lesovik scattering approach, Annals of Physics 422, 168298 (2020).
- J.Strečka, O.Krupnitska, J.Richter, Investigation of entanglement measures across the magnetization process of a highly frustrated spin-1/2 Heisenberg octahedral chain as a new paradigm of the localized-magnon approach, Europhys. Lett. 132, 30004 (2020).
- R.Ya.Stetsiv, One-particle spectral densities and phase diagrams of one-dimensional proton conductors, Condensed Matter Physics 24, 23704 (2021).
- A.P.Moina, Polarization rotation by external electric field in the two-dimensional antiferroelectric squaric acid H2C4O4, Phys. Rev. B 103, 214104 (2021).
- T.Krokhmalskii, T.Hutak, O.Rojas, S.M. de Souza, O.Derzhko, Towards low-temperature peculiarities of thermodynamic quantities for decorated spin chains, Physica A 573, 125986 (2021).
- Ya.Shchur, A.V.Kityk, V.V.Strelchuk, A.S.Nikolenko, N.A.Andrushchak, P.Huber, A.S.Andrushchak, Paraelectric KH2PO4 nanocrystals in monolithic mesoporous silica: Structure and lattice dynamics, Journal of Alloys and Compounds 868, 159177 (2021).
- J.Strečka, K.Karl’ová, O.Krupnitska, On the failure of effective-field theory in predicting a spurious spontaneous ordering and phase transition of Ising nanoparticles, nanoislands, nanotubes and nanowires, Physica E 133, 114805 (2021).