Current
research
BRIEF CHARACTERISTICS OF THE
RESEARCH ACTIVITIES
The principal research objective of the condensedmatter theory group is a reliable and controllable microscopic description of electronic and atomic properties of solids, in particular of complex systems with nontrivial elementary cells, broken symmetries, in and out of thermodynamic equilibrium or in extreme conditions. Based on the research experience and expertise of the research personnel, advanced modern methods from quantum equilibrium and nonequilibrium statistical mechanics, Greenfunction formalism, electronic structure calculations, and numerical simulations are developed, improved and employed to determine qualitative model and quantitative realistic materials properties.
FIELDS OF RESEARCH INTERESTS
Abinitio electronic structure calculations
Electronic structure of complex materials with unusual properties is studied
with TBLMTO, FPLAPW, and pseudopotential abinitio densityfunctional methods.
The calculations are used to predict new materials with potential applications.
Relativistic effects and correlationinduced dynamical fluctuations in the electronic
structure of alloys, surfaces, interfaces, interlayers and multilayers are taken into account.
Realspace finiteelement method applicable to nonperiodic structures is being developed.
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Dilute magnetic semiconductors
Dilute magnetic semiconductors are prototype materials
with structural, magnetic, transport, and optical properties determined
by combined effects of disorder, electron correlations, and hybridization.
Our theoretical study, based on densityfunctional theory, aims at facilitating
magnetic behavior of DMS by optimizing the electronic structure
and by controlling native defects and intentional codoping.
Starting from (Ga,Mn)As, we are interested in nontraditional DMS based, e.g., on
mixed IIIV semiconductors and IIIV compounds.
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Mappings of abinitio systems on effective models
A mapping of
the total energy of electrons in magnetic materials and alloys on Heisenberg
and Isinglike 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 nonmagnetic substrate.
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Strong electron correlations
Electron correlations are studied in tightbinding models with a screened local
interaction of the Hubbard type.
Advanced summation methods of Feynman diagrams for twoparticle Green functions
are the core of our interest.
Various simplified forms of parquet equations mixing selfconsistently
multiple electronelectron and electronhole scatterings are used to describe
peculiarities of the strongcoupling regime.
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Quantum critical behavior and phase transitions in itinerant systems
Lowtemperature quantum critical behavior where two or more noncommuting operators
remain relevant are studied with manybody diagrammatic techniques.
The objective is to understand and quantitatively describe admissible types of
the critical behavior of vertex functions in interacting and disordered
itinerant systems.
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Quantum coherence in nonequilibrium systems and nanostructures
Quantum coherence due to cooperative scatterings is studied.
Of particular interest are effects of backscatterings on bulk transport properties
of electrons in disordered media.
Effects of decoherence and dephasing of electrons interacting with optical phonons
in quantum dots out of equilibrium are examined with nonequlibrium Green functions and
transport equations.
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Timeresolved spectroscopy
Timeresolved spectroscopy is another domain of quantum coherence.
Interband excitation of electrons by strong femtosecond pulses
and immediate electron response and relaxation are studied
theoretically for the case of disordered semiconductors.
The results, showing a competition between light
and disorder scattering, represent not only a simple but
representative simulation of the behavior of interacting systems,
but also serve as a basic reference for testing transport equations.
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Surface nanostructure
Structural properties and mechanism of formation of surface nanostructure of metals,
semiconductors, and multicomponent materials are studied by numerical simulations.
Molecular dynamics and MonteCarlo simulations are combined to achieve a multiscale
description of the critical behavior of relevant statistical mechanical quantities.
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Statistical physics of random systems and nonequilibrium thermodynamics
Theory of random systems, in particular spin glasses, is pursued.
Microscopic approaches bases on the realreplica method combined with TAP equations
are used to understand the meanfield theory of spin glasses.
In nonequilibrium systems dynamical fluctuations in irreversible processes, variational formulation
of nonequilibrium steady states and nonequilibrium thermodynamics beyond
linear response are investigated.
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Econophysics
Evolutionary games with particular emphasis on the Minority Game and its variants
are investigated.
Development of nontrivial spatial structures and dynamical spinglass like phases
there are studied with predominantly numerical simulations.
Also analytical calculations using the replica method have been initiated.
Beyond this, the socalled Maslov model for stockmarket fluctuations is currently scrutinized.
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