Full-text resources of PSJD and other databases are now available in the new Library of Science.
Visit https://bibliotekanauki.pl
Preferences help
Polish version English version Language
enabled [disable] Abstract
Number of results

Results found: 7

Number of results on page
first rewind previous Page / 1 next fast forward last

Search results

help Sort By:

help Limit search:
first rewind previous Page / 1 next fast forward last
1
Content available remote

Beyond the Virtual Crystal Approximation in Diluted Magnetic Semiconductors

100%
Tworzydło J.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 2
391-394
EN
We present a new model approach which goes beyond the virtual crystal approximation and the molecular field approximation in the description of the spin splitting of band states in diluted magnetic semiconductors. The theory is formulated within a one-band effective mass approximation and explicitly takes into account a chemical and magnetic disorder caused by substitutional ions. The results confirm the apparent dependence of the p-d exchange integral on x in Cd_{1-x}Mn_{x}S for small concentrations of Mn ions and we predict the asymmetric field and temperature dependence of the spin splitting in this compound.
2
Content available remote

Beyond Virtual Crystal and Molecular Field Approximations in Diluted Magnetic Semiconductors

100%
Tworzydło J.
Acta Physica Polonica A
|
1995
|
vol. 88
|
issue 4
655-662
EN
The framework of the virtual crystal approximation and the molecular field approximation has been widely used in the description of the extended states affected by the presence of the p-d exchange interaction in diluted magnetic semiconductors. We review shortly the known examples of diluted magnetic semiconductors systems which are described beyond these approx­imations. The interesting case constitutes the nearly binding impurity po­tential in Cd_{1-x}Μn_{x}S. The lattice approaches developed earlier allowed to prove in this case the breakdown of the virtual crystal approximation for low concentrations of magnetic ions and to explain the apparent concentra­tion dependence of the exchange integral. We take explicitly into account the substitutional disorder neglected in the lattice theories and we rederive these results within the dilute and the average t-matrix alloy approach. We generalize systematically this theory to include also the magnetic disorder of the dilute spin subsystem appearing at finite temperatures. When the off-diagonal exchange scattering terms are taken into account in our calcula­tions, we get a good agreement with the experimental data on the asymmetric field dependent spin splitting and the zero-field concentration dependence of the energy gap.
3
Content available remote

Landau Levels of Double-Weyl Nodes in a Simple Lattice Model

63%
Rechciński R., Tworzydło J.
Acta Physica Polonica A
|
2016
|
vol. 130
|
issue 5
1179-1182
EN
In the Weyl semimetals, a recently discovered class of bulk materials, inverted band gap closes in the first Brillouin zone at topologically protected points of degeneracy called the Weyl nodes. By using the Chern number formalism it is possible to assign to each of the nodes an integer topological charge Q. While around typical Weyl points the energy disperses linearly in all three directions, double-Weyl nodes (with |Q|=2) exhibit quadratic dispersion in two directions and linear in the third one. We use a simple 2-band tight-binding lattice model to investigate the dispersion of the Landau levels in the presence of quantizing magnetic field in the vicinity of a double-Weyl node. In the long wavelength limit we obtain analytically the expected presence of two chiral levels. In addition, we find numerous level crossings between the non-chiral Landau levels and the chiral ones, a feature which is distinct from the single node case. Calculations for a finite-size sample, both with periodic and hard-wall boundary conditions (the latter corresponding to slab geometry), show that the two chiral levels hybridize in the conduction band with the two lowest non-chiral Landau levels. In the case of slab geometry these four levels are responsible for the formation of a protected surface state.
4
Content available remote

Magnetooptical Properties of GaAs:Mn

39%
Szczytko J., Stachow A., Mac W., Twardowski A., Becla P., Tworzydło J.
Acta Physica Polonica A
|
1996
|
vol. 90
|
issue 5
951-954
EN
Magnetoreflectance from GaAs:Mn was measured in the free exciton range for B ≤ 5 T and T = 2.0 K. Combining optical results with magnetization data the value for the exchange parameter N_{0}α-N_{0}β =-(2.3 ± 0.6) eV was obtained. Assuming that N_{0}α ≈ +0.2 eV, the ferromagnetic p-d exchange interaction was found with the magnitude N_{0}β ≈ +2.5 eV.
5
Content available remote

Controlling Structural and Functional Features of Photosynthetic Antenna

39%
Fiedor L., Fiedor J., Pilch M., Susz A., Tworzydło J., Michalik M.
Acta Physica Polonica A
|
2012
|
vol. 122
|
issue 2
255-258
EN
In order to gain control over the assembly and functioning of photosynthetic antenna, we have developed methods to manipulate pigment composition of bacterial LH1 complexes via their reconstitution with modified bacteriochlorophylls or carotenoids, major photoactive cofactors of these antennae. In the present work we show how the reconstitution and pigment exchange approach is applied to control structural and functional parameters of LH1 and its subunits. The size of the subunits and the energy of the first excited singlet state can be controlled via the use of detergent while the thermodynamics of LH1 formation can be modified using carotenoids and/or a co-solvent. Carotenoids affect the efficiency of the intracomplex energy transfer, while the replacement of native bacteriochlorophyll a with its Ni-substituted analog allows one to control the excited state properties of LH1. These results show that LH1 is a very promising model system applicable for the design of bio-inspired device performing solar energy conversion.
6
Content available remote

Effects of the Spin-Dependent Potential fluctuations on Free Exciton Zeeman Splitting of Zn_{1-x}Mn_{x}Se

39%
Herbich M., Mac W., Stachow A., Twardowski A., Tworzydło J., Demianiuk M.
Acta Physica Polonica A
|
1996
|
vol. 90
|
issue 4
813-816
EN
Magnetoreflectance of free exciton and magnetization in Zn_{1-x}Mn_{x}Se (0.0007 < x < 0.12) were measured. The evaluated proportionality factor between the exciton splitting and the magnetization showed a strong concentration dependence. This effect cannot be explained within the mean field approximation and the virtual crystal approximation and it was described within the model including chemical and magnetic disorder.
7
Content available remote

Transport Properties of Disordered Graphene Layers

39%
Gryglas-Borysiewicz M., Jouault B., Tworzydło J., Lewińska S., Strupiński W., Baranowski J.
Acta Physica Polonica A
|
2009
|
vol. 116
|
issue 5
838-840
EN
Samples consisting of a few layers of graphene obtained by thermal decomposition of SiC were studied by means of transport experiments at 4 K and in a magnetic field up to 7 T. Transport data show that the samples have a two-dimensional character. Magnetoresistance has an approximately linear character at high magnetic fields, which has been previously observed in graphite samples, and a negative magnetoresistance, at low magnetic fields. The transverse resistivity ρ_{xy} is nonlinear as a function of B, which can be described using a many-carrier model.
first rewind previous Page / 1 next fast forward last
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.