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Present & past research interests at a glance

Carbon and related materials

  • Carbon nanotubes growth

    Materials science of carbon nanotubes (CNTs) is the meeting point of various paradigms from fundamental and applied physics and chemistry. Understanding how such a multitude of concepts ticks together to make the CNT possible is still a challenge to both experiment and theory...

  • Graphene, graphane, etc.

    Complementary electronic properties and a tendency to form sharp graphene−graphane interfaces open tantalizing possibilities for two-dimensional nanoelectronics. Employing first-principles density functional and tight-binding calculations we have shown that graphane can serve as natural host for graphene quantum dots--clusters of vacancies in the hydrogen sublattice.

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Semiconductor surfaces, crystal growth

  • Self-assembled quantum dots
  • Reconstructions of low-index III-V surfaces
  • Surface chemical reactions

    Ruling processes in MBE of III-V semiconductors Self-organized quantum-dot heterostructures, or simply quantum dots (QDs), have left their “teens” behind. The high technological promises they have brought to optoelectronics have triggered an enormous scientific activity. As a representative example one can take the work on the InAs/GaAs lattice-mismatched heteroepitaxial system. In terms of the observed resultant morphology, the epitaxy of QDs [e.g., molecular beam epitaxy (MBE), or metal-organic chemical vapor deposition (MOCVD)] follows the Stranski-Krastanov growth mode. Though our knowledge on the nature of the Stranski- Krastanov regime has considerably increased, both experimentalists and theorists were still on the way to complete understanding the intricacies of QD growth kinetics. System-specific, microscopic information in this respect was a must. Important information comes from direct experimental probes, like in situ scanning tunneling microscopy (STM), reflection high-energy electron diffraction (RHEED), or reflectance-difference spectroscopy (RDS). However, if one is aiming at a complete understanding of QD growth, the information accessible from experiments may not be sufficient. This is particularly true if one focuses on the characteristics of species dynamics at the surface, details of the surface atomic structure, thermodynamic quantities, etc.
    We have addressed InAs heteroepitaxy on GaAs(001)—the III-V semiconductor system of ultimate importance for QD “self-fabrication”. An extensive track record of experimental studies has established a number of anomalies in the QD self-assembly for this system. It was also brought out clearly that any theory has to capture the subtleties of strain-dependent QD growth kinetics. Thus the first fundamental questions to be answered were how strain affects surface morphology, and its impact on surface adatom mobility. The characteristic length and time scales for the latter lie in the microscopic range, 0.1– 10 Angstroms and fs--ps, where the density-functional theory (DFT) is one of the most commonly used theoretical tools. We have developed an appropriate theoretical framework, building on DFT, to tackle the above mentioned problems in InAs/GaAs(001) heteroepitaxy.

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Physics of conventional and high-Tc superconductivity

  • Pairing mechanisms
  • Phenomenology of electrodynamic response
  • Fluctuations

s-d intra-atomic exhange The discovery of high-temperature superconductivity in cuprates and the subsequent "research rush" have led to the appearance of about 100000 papers to date. Virtually every fundamental process known in condensed matter physics was probed as a possible mechanism of this phenomenon. Nevertheless, none of the theoretical efforts resulted in a coherent picture. For the conventional superconductors the mechanism was known to be the interaction between electrons and crystal-lattice vibrations, but the development of its theory lagged behind the experimental findings. The case of cuprate high-Tc superconductivity appears to be the opposite: we do not convincingly know which mechanism is to be incorporated in the traditional Bardeen-Cooper-Schrieffer (BCS) theory. Thus the path to high-Tc superconductivity in cuprates, perhaps carefully hidden or well-forgotten, has turned into one of the long-standing mysteries in physical science.

In contrast with all previous proposals, we have advanced the intra-atomic exchange of two electrons between the 4s and 3dx^2-y^2 states of the Cu atom as the origin of high-Tc superconductivity in the layered cuprates and have shown that the basic spectroscopic and thermodynamic experiments can be explained by it.

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Biomembranes, protein structure and folding

  • Coarse-grained modeling of lipid bilayerscoarse-grained lipid bilayer
  • Protein secondary structure
  • Algorithms for global optimization of biomolecular systems

Within the research focusing on protein secondary structure formation, we have introduced the infinite helix as a valuable reference limiting case that can be used to critically assess, compare, and improve the parametrization of empirical force fields commonly used in biomolecular simulations. By comparing Density Functional Theory and force field results we also illustrate in a simple manner the importance of improving the description of the van der Waals interactions in both methodologies.

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