Fyzikální ústav Akademie věd ČR

Research subjects at department 23

Ab-initio electronic structure calculations

Electronic structure of complex materials with unusual properties is studied with TB-LMTO, FP-LAPW, and pseudopotential ab-initio density-functional methods. The calculations are used to predict new materials with application potential. Relativistic effects and correlation-induced dynamical fluctuations in the electronic structure of alloys, surfaces, interfaces, interlayers and multilayers are taken into account. Real-space finite-element method applicable to nonperiodic structures is being developed.   The full text >>

Non-traditional magnetic semiconductors

Based on our experience with dilute magnetic semiconductors, we use density-functional calculations to do a systematic theoretical research of new materials combining semiconducting and magnetic properties. We were the first to show theoretically that I-Mn-V compounds are semiconductors with a stable antiferromagnetic arrangement of Mn local magnetic moments while the corresponding diluted systems I-(II,Mn)-V can be turned into a ferromagnetic state at sufficiently high concentration of carriers.  The full text >>

Statistical physics of random systems and nonequilibrium thermodynamics

Theory of random systems, in particular spin glasses, is pursued. Microscopic approaches bases on the real-replica method combined with Thouless-Anderson-Palmer equations are used to understand the mean-field theory of Ising and other spin glass models. Genesis of the full solution with a continuous replica-symmetry breaking is pursued in the asymptotic region below the transition to the glassy phase.  The full text >>

Quantum coherence in disordered systems

Quantum coherence due to correlated scatterings of electrons on random impurities is studied. We We develop new Green function techniques so that to describe reliably effects of backscatterings on bulk transport properties of electrons in disordered media. The principal objective is to achieve a consistent theory of the disorder-induced vanishing of diffusion, the phenomenon known as Anderson localization.   The full text >>

Strong electron correlations

Electron correlations are studied in tight-binding models with a screened local interaction of the Hubbard type. Advanced summation methods of Feynman diagrams for two-particle Green functions are the core of our interest. Various simplified forms of parquet equations mixing self-consistently multiple electron-electron and electron-hole scatterings are used to describe peculiarities of the strong-coupling regime.   The full text >>

Mappings of ab-initio systems on effective models

A mapping of the total energy of electrons in magnetic materials and alloys on Heisenberg and Ising-like models is utilized to describe bulk and surface magnetic ordering. The theory is applied to dilute metallic and semiconducting magnetic materials, phase diagrams of layers of alloys, and theoretical explanation of ferromagnetism of thin films on a non-magnetic substrate.   The full text >>

Surface nanostructures

Structural properties and mechanisms of formation of surface nanostructure on metal as well as semiconductor substrates are investigated by numerical simulations. The objective is to explain formation of nanostructures on the microscopic level and by this provide interpretation of resent experiments. Molecular dynamics and Monte-Carlo simulations are combined with approximative analytical methods to achieve description of relevant statistical mechanical quantities during growth by molecular beam epitaxy or by pulsed laser   The full text >>

Quantum critical behavior and phase transitions in itinerant systems

Low-temperature quantum critical behavior where two or more noncommuting operators remain relevant are studied with many-body diagrammatic techniques. The objective is to understand and quantitatively describe admissible types of the critical behavior of response vertex functions in interacting and disordered quantum itinerant systems.   The full text >>

Spin-dependent transport properties

We curretly study complex transport properties of magnetic metals and, in particular, magnetic systems with disorder from first principles. Studied properties include resistivity due to the spin-disorder at finite temperatures as well as complex phenomena which originate from relativistic effects. We concentrate on properties like Seebeck and Nernst effects, anisotropic magnetoresistance, anomalous Hall effect, Gilbert damping, etc.   The full text >>

Transient dynamics of electrons in mesoscopic and bulk systems

This research concentrates on the electron response to sudden/fast changes of boundary conditions, like coupling to the particle reservoirs (leads) and to the environment (thermal baths), or to the excitation by short external pulses of light or other fields. The research aims at an adequate description of the non-equilibrium correlated state during the initial transient, the decay of correlations as a gate to the non-equilibrium kinetic stage of evolution and to the final equilibration.   The full text >>

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