Department of Fundamental Research

Head of department prof., dr.  Vladas Vansevičius
prof., dr. Vladas Vansevičiusphone +370 5 2619466

Main goals of the department:
1. Theoretical investigations and modelling of chaotic systems, neural networks, and nanostructures.
2. Theoretical and experimental investigations of fluctuations, hot electron and phonon dynamics.
3. Theoretical and observational investigations of complex megasystems. 

Research directions of the department:
1. Complex neural networks and desynchronization algorithms.
2. Chaos control algorithms.
3. Classical and quantum electron systems.
4. Terahertz radiation sources.
5. Fluctuations and dynamics of coupled electron-phonon systems.
6. Plasmons in dynamics of highly excited electrons and phonons.
7. Spectrophotometry of megasystems.
8. Chemodynamical evolution of complex megasystems.


Equipment, Software and methods

Nonlinear Dynamics and Nanophysics Laboratory

The analysis of nonlinear dynamics, quantum and kinetic problems are performed by means of various approximate analytical (a method of separation of fast and slow motions, averaging method, phase reduction method, etc.) as well as numerical (algorithms of numerical integration of differential equations, Monte Carlo method, etc.) methods

Fluctuation research laboratory

Nanosecond gated microwave X-band/Ka band modulation-type radiometric setup for measurement of hot-electron fluctuations at microwave frequencies. On-wafer measurements at room temperature are conducted using coaxial probe station. Waveguide probing can be used instead at a liquid nitrogen temperature. Fluctuations are measured only during the short pulse and that enables the research of kinetic processes in semiconductors. Voltage pulse duration ranges from 10 nanoseconds to 15 microseconds. Electric fields can exceed 100 kV/cm. Joule heating becomes unimportant because of short pulses.

Capacitance-voltage (50 kilohertz – 30 megahertz) and voltage-current measurement system available. It can be used for electron gas profile estimation in the 2DEG transistor channels as well as finding of 2DEG density.   

Agilent–Süss–Maury spectrometer for transistor on wafer measurements of microwave response and noise spectra and microwave power at frequencies from 0.1 to 50 GHz. The main direction – SiGe heterobipolar transistors and GaN heterostructure field effect transistors.

Nanosecond voltage-pulse setup (pulse duration 0.2...100 ns) is used for hot-electron drift velocity measurements in electric field range up to 300 kV/cm. Channel self-heating effects are minimized.  

Electro-magnet (2 Tesla)  

Monte Carlo and other codes are available for numerical simulation of hot-electron fluctuations in semiconductor heterostructures and transistors.

  • Nonlinear Dynamics and Nanophysics Laboratory
    Research Council of Lithuania, the project “Synchronization and chaos control algorithms for nonlinear systems using periodically switched time-delayed feedback”, project leader prof. K. Pyragas (2014–2017).
    The project deals with control algorithms based on periodically switched time-delayed feedback and their application to the problems of chaos control (stabilization of unstable periodic orbits), the anticipating synchronization problems, and the problems of desynchronizing the neural networks.
  • Fluctuation research laboratory
    Research Council of Lithuania, project “Optimal power-reliability trade-off in quantum well channels”, prof. A. Matulionis (2016-2019).
    Project research is focused on the GaN and its (In,Al) compounds as well as on ZnO (which have many similar properties to GaN) and its (Be,Mg) compounds based quantum channels. The aim is an optimisation of HEMT quantum channels for the best power-reliability trade-off.
  • Electronic Structure Theory Laboratory
    M-ERA.NET project „Metrology at the nanoscale with diamonds“ („MyND“), leader of the Lithuanian partner is dr. Audrius Alkauskas, the coordinator of the project is prof. Ruvin Feber (University of Latvia) (2015–2018).
    The project conducted together with the Laser Center of the University of Latvia and Latvian Solid State Physics Institute. The project is devoted to the use of point defects in diamond (so-called NV centers) for detected of varying magnetic fields at the nanoscale.
  • Megasystem physics laboratory
    1. Research Council of Lithuania, the project „Low‐Mass Dwarf Galaxy Evolution” of the national research program „Towards future technologies”, project leader prof. V. Vansevičius (2016–2018).
    The main objective of the project is to reveal the evolution of isolated galaxies residing in low‐mass dark matter haloes from the early Universe to the present day.

    2. Research Council of Lithuania, the project “Star Formation in Galaxy Disks: Global vs. Local“, project leader dr. D. Narbutis (2015–2018).
    The project aims to determine spatial and dynamical parameters of ongoing star formation in the galaxy NGC598 disk by coordinated use of observational data obtained with ground- and space-based telescopes.

Most important publications
Fluctuation research laboratory
  1. Jakštas Vytautas, Grigelionis Ignas, Janonis Vytautas, Valušis Gintaras, Kašalynas Irmantas, Seniutinas Gediminas, Juodkazis Saulius, Prystawko P., Leszczyński J. Electrically driven terahertz radiation of 2DEG plasmons in AlGaN/GaN structures at 110 K temperature. Applied physics letters. ISSN 0003-6951. vol. 110, iss.20 (2017), p. art. no. 202101 p.1-5.
  2. Ardaravičius Linas, Kiprijanovič Oleg, Liberis Juozapas, Ramonas Mindaugas, Šermukšnis Emilis, Matulionis, Arvydas, Toporkov M., Avrutin V., Özgür Ü., Morkoç H. High-field electron transport in doped ZnO. Materials research express. ISSN 2053-1591. vol.4, iss.6 (2017), p. art. no. 066301 p. 1-6.
  3. Voß Daniel, Zouaghi Wissem, Jamshidifar Mehran, Boppel Sebastian, McDonnell Cormac, Bain James R. P., Hempler Nils, Malcolm Graeme P. A., Maker Gareth T., Bauer Maris, Lisauskas Alvydas, Rämer Adam, Shevchenko Sergey A., Heinrich Wolfgang, Krozer Viktor, Roskos Hartmut G. Imaging and spectroscopic sensing with low-repetition-rate terahertz pulses and GaN teraFET detectors. Journal of infrared, millimeter and terahertz waves. ISSN 1866-6892. 2018, vol. 39, iss.3, p. 262-272.
  4. Šermukšnis Emilis, Liberis Juozapas, Matulionis Arvydas, Avrutin V., Toporkov M., Özgür Ü., Morkoç H. Hot LO-phonon limited electron transport in ZnO/MgZnO channels. Journal of applied physics. ISSN 0021-8979. 2018, vol. 123, iss. 17, art. no. 175702, p. 1-9.
Nonlinear Dynamics and Nanophysics Laboratory
  1. Tatjana Pyragienė, Kęstutis Pyragas. Anticipatory synchronization via low-dimensional filters. Physics letters. A. ISSN 0375-9601. vol. 381, iss. 22 (2017), p. 1893-1898.
  2. Irmantas Ratas, Kęstutis Pyragas. Symmetry breaking in two interacting populations of quadratic integrate-and-fire neurons. Physical review. E, Statistical, nonlinear, and soft matter physics. ISSN 2470-0045. vol. 96, iss.4 (2017), p. art. no. 042212 p. 1-9.
  3. Viktoras Pyragas, Kęstutis Pyragas. Act-and-wait time-delayed feedback control of autonomous systems. Physics letters. A. ISSN 0375-9601. 2018, vol. 382, iss. 8, p. 574-580.
  4. Kęstutis Pyragas, Augustinas Povilas Fedaravičius, Tatjana Pyragienė. Optimal waveform for entrainment of a spiking neuron with minimum stimulating charge. Physical Review E. ISSN 2470-0045. 2018, vol. 98, iss. 4, art. no. 042216, p. 1-14.
  5. Novičenko Viktor, Ratas Irmantas. In-phase synchronization in complex oscillator networks by adaptive delayed feedback control. Physical review E. ISSN 2470-0045.2018, vol. 98, iss. 4, art. no. 042302, p. 1-11.
  6. Irmantas Ratas, Kęstutis Pyragas. Macroscopic oscillations of a quadratic integrate-and-fire neuron network with global distributed-delay coupling. Physical review E. ISSN 2470-0045. 2018, vol. 98, iss. 5, art. no. 052224, p. 1-11.
  7. Pyragas Viktoras, Pyragas Kęstutis. State-dependent act-and-wait time-delayed feedback control algorithm. Communications in nonlinear science and numerical simulation. ISSN 1007-5704. 2019, vol. 73, p. 338-350.
Megasystem physics laboratory
  1. Philippe de Meulenaer, Rima Stonkutė, Vladas Vansevičius. Deriving physical parameters of unresolved star clusters - V. M 31 PHAT star clusters. Astronomy & astrophysics. ISSN 0004-6361. vol. 602 (2017), p. art. no. A112 [1-8].
  2. Zubovas Kastytis, Bourne Martin A. Do AGN outflows quench or enhance star formation? Monthly notices of the Royal astronomical society. ISSN 0035-8711. vol. 468, iss.4 (2017), p. 4956-4967.
  3. Kastytis Zubovas. Massive outflow properties suggest AGN fade slowly. Monthly notices of the Royal astronomical society. ISSN 0035-8711. 2018, vol. 473, iss.3, p. 3525-3535.
  4. Gudas Rimtautas, Šiupšinskas Laimonas, Gudaitė Agnė, Vansevičius Vladas, Stankevičius Edgaras, Smailys Alfredas, Vilkytė Akvilė, Simonaitytė Rasa. The Patello-femoral joint degeneration and the shape of the patella in the population needing an arthroscopic procedure. Medicina. ISSN 1010-660X. 2018, vol. 54, no. 2, p. 1-8.
  5. Kastytis Zubovas. AGN must be very efficient at powering outflows. Monthly notices of the Royal astronomical society. ISSN 0035-8711. 2018, vol. 479, iss. 3, p. 3189-3196.
  6. Nardini Emanuele, Zubovas Kastytis. Multi-phase outflows as probes of AGN accretion history. Monthly notices of the Royal astronomical society. ISSN 0035-8711. 2018, vol. 478, iss. 2, p. 2274-2280.
  7. Nayakshin Sergei, Zubovas Kastytis. Sgr A* envelope explosion and the young stars in the centre of the Milky Way. Monthly notices of the Royal astronomical society. ISSN 0035-8711. 2018, vol. 478, iss. 1, p. 127-131.
  8. Eimantas Ledinauskas, Kastytis Zubovas. Reignited star formation in dwarf galaxies that were quenched during reionization. Astronomy & astrophysics. ISSN 0004-6361. 2018, vol. 615, art. no. A64, p. 1-10.
  9. Stonkutė Rima, Čeponis Marius, Leščinskaitė Alina, Naujalis Rokas, Vansevičius Vladas. Dwarf irregular galaxy Leo A extends even farther, according to HST WFC3 photometry. Astronomy & astrophysics. ISSN 0004-6361. 2018, vol. 614, art. no. A144, p. 1-5.
  10. Jonas Bialopetravičius, Donatas Narbutis, Vladas Vansevičius. Deriving star cluster parameters with convolutional neural networks. I. Age, mass, and size. Astronomy & astrophysics. ISSN 0004-6361. 2019, vol. 621, art. no. A103, p. 1-10.
Electronic Structure Theory Laboratory
  1. Exarhos Annemarie L., Hopper David A., Grote Richard R., Alkauskas Audrius. Bassett, Lee C. Optical signatures of quantum emitters in suspended hexagonal boron nitride. ACS Nano. ISSN 1936-0851. vol. 11, iss.3 (2017), p. 3328-3336.
  2. Biktagirov T.B., Smirnov A.N., Davydov V.Yu., Doherty M.W., Alkauskas Audrius, Gibson B.C., Soltamov V.A. Strain broadening of the 1042-nm zero-phonon line of the NV center in diamond: a promising spectroscopic tool for defect tomography. Physical review. B. ISSN 2469-9950. vol. 96, iss. 7 (2017), p. art. no. 075205 p. 1-7.
  3. Frodason Y.K., Johansen K.M., Bjørheim T.S., Svensson B.G., Alkauskas Audrius. Zn vacancy as a polaronic hole trap in ZnO. Physical review. B. ISSN 2469-9950. vol. 95, iss. 9 (2017), p. art. no. 094105 p. 1-8.
  4. Lyons John L., Alkauskas Audrius, Janotti A., Van de Walle Chris G. Deep donor state of the copper acceptor as a source of green luminescence in ZnO. Applied physics letters. ISSN 0003-6951. vol. 111, iss. 4 (2017), p. art. no 042101 p. 1-4.
  5. Shen Jimmy-Xuan, Wickramaratne Darshana, Dreyer Cyrus E., Alkauskas Audrius, Young Erin, Speck James S., Van de Walle Chris G. Calcium as a nonradiative recombination center in InGaN. Applied physics express. ISSN 1882-0778. vol. 10, iss. 2 (2017), p. art. no 021001 p. 1-3.
  6. Pfender Matthias, Aslam Nabeel, Simon Patrick, Antonov Denis, Thiering Gergő, Burk Sina, de Oliveira Felipe Fávaro, Denisenko Andrej, Fedder Helmut,Meijer Jan, Garrido Jose A., Gali Adam, Teraji Tokuyuki, Isoya Junichi, Doherty Marcus William, Alkauskas Audrius, Gallo Alejandro, Grüneis Andreas, Neumann Philipp, Wrachtrup Jörg. Protecting a diamond quantum memory by charge state control. Nano Letters. ISSN 1530-6984. eISSN 1530-6992. 2017, vol. 17, Iss. 10, p. 5931-5937.
  7. Frodason Y. K., Johansen K. M., Bjørheim T. S., Svensson B. G., Alkauskas Audrius. Zn vacancy-donor impurity complexes in ZnO. Physical review B. ISSN 2469-9950. 2018, vol. 97, iss. 10, art. no. 104109, p. 1-8.
  8. Weston L., Wickramaratne D., Mackoit-Sinkevičienė Mažena, Alkauskas Audrius, Van de Walle C. G. Native point defects and impurities in hexagonal boron nitride. Physical review B. ISSN 2469-9950. 2018, vol. 97, iss. 21, art. no. 214104, p. 1-13.
  9. Wickramaratne Darshana, Shen Jimmy-Xuan, Alkauskas Audrius, Van de Walle Chris G. Comment on “Comparative study of ab initio nonradiative recombination rate calculations under different formalisms”. Physical review B. ISSN 2469-9950. 2018, vol. 97, iss. 7, art. no. 077301, p. 1-3.
  10. Londero Elisa, Thiering Gergo, Razinkovas Lukas, Gali Adam, Alkauskas Audrius. Vibrational modes of negatively charged silicon-vacancy centers in diamond from ab initio calculations. Physical review B. ISSN 2469- 9950. 2018, Vol. 98, iss. 3, art. no. 035306, p. 1-9.
  11. Dreyer Cyrus E., Alkauskas Audrius, Lyons John L., Janotti Anderson, Van de Walle Chris G. First-principles calculations of point defects for quantum technologies. Annual review of materials research. ISSN 1531-7331. 2018, vol. 48, p. 1-26.
  12. Proscia Nicholas V., Shotan Zav, Jayakumar Harishankar, Reddy Prithvi, Cohen Charles, Dollar Michael, Alkauskas Audrius, Doherty Marcus, Meriles Carlos A., Menon Vinod M. Near-deterministic activation of room-temperature quantum emitters in hexagonal boron nitride. Optica. ISSN 2334-2536. 2018, vol. 5, iss. 9, p. 1128-1134.
  13. Darshana Wickramaratne, Cyrus E. Dreyer, Bartomeu Monserrat, Jimmy-Xuan Shen, John L. Lyons, Audrius Alkauskas, Van de Walle Chris G. Defect identification based on first-principles calculations for deep level transient spectroscopy. Applied physics letters. ISSN 0003-6951.2018, vol. 113, iss. 19, art. no. 192106, p. 1-5.