Fyzikální ústav Akademie věd ČR

Selected results of department 23

Microscopic Analysis of the Valence Band and Impurity Band Theories of (Ga,Mn)As

We resolved a long-standing controversy between the valence-band and impurity-band picture of diluted magnetic semiconductors (Ga,Mn)As. We calculated the electron density of states for varying content of Mn and showed that no detached impurity band is formed in ferromagnetic materials. The dependence of the Fermi energy on chemical composition is consistent with observed blue shift in infrared absorption spectra and magnetic circular dichroism. The full text >>

Monotonic return to steady nonequilibrium

We analyze how to construct Lyapunov functions describing relaxation to the stationary regime of thermodynamically open systems. These functions are time-monotonous and they can conveniently be applied to the study of stability of stationary states - examples are the free energy in equilibrium respectively the entropy production in weakly non-equilibrium systems. The main result is a proposal of a new Lyapunov function for certain far from equilibrium models, via the dynamical theory of fluctuations. The full text >>

Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds

Based on density functional calculations of electronic structure and magnetic ordering we proposed that LiMnAs and related I-Mn-V crystals are antiferromagnetic semiconductors with bandgap around 1 eV. The antiferromagnetic state of these compouns is not sensitive even to high level of doping and the estimated Neel temperature is well well above the room temperature. This, together with a remarkable calculated magnetic anisotropy, makes these materials attractive for spintronics applications. The full text >>

Elastically scattered electrons on impurities

The standard approach to the calculation of the electronic structure in disordered solids is the mean-field, coherent-potential approximations. Although rather successful for electronic spectra, this approximation fails in the description of backscattering effects on transport properties. We applied an expansion beyond the mean-field approximation and evaluated the leading-order vertex corrections to the electrical conductivity for electrons scattered either on quenched random or thermally equilibrated impurities. The full text >>

Towards theory of Heusler alloys

We have been studying a broad class of relevant physical properties of Heusler alloys, in particular, their magnetic structure as a function of temperature and disorder. We calculate magnetic moments, magnon spectra, the spin-stiffness constant, and critical (Curie) temperatures, as well as the transport properties. Besides that we investigate Heusler alloys at the hydrostatic pressure with the aim of deeper understanding of their properties. The transport properties, in particular, are very sensitive to the presence of any kind of disorder and to temperature. The full text >>

Effect of persistence of compact surface clusters during pulsed-laser deposition on submonolayer growth

We predicted a new shape of the temperature dependence of island density for Pulse Laser Deposition. The shape is characterized by alternation of regions of fast decrease and plateaus corresponding to existence of small stable islands. This effect is caused by changing of a relation between cluster decay time and interval between pulses with temperature.
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Correlated initial condition for an embedded process by time partitioning

The early stages of fast transients in electron systems are controlled by the initial conditions. Their incorporation into a theoretical description using the non-equilibrium Green’s functions is possible by means of the technique of the partitioning-in-time. B. Velický, A. Kalvová and V. Špička, Phys. Rev. B 81, 235116 (2010). The full text >>