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3 Acta Physica Polonica A

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Surface Metallic Pattern for Enhancement of a THz Field in a Two-Dimensional Electron Plasma

100%

Tarkowski T. , Łusakowski J.

Acta Physica Polonica A

2017

tom 132

nr 2

332-334

A metamaterial in the form of a periodic lattice of split-ring resonators on a GaAs/AlGaAs heterostructure was numerically studied at terahertz frequencies. A finite-difference time-domain algorithm was applied to calculate distribution of the electromagnetic field in the layer positioned at 100 nm below the heterostructure surface where a two-dimensional electron gas typically resides in real structures. The results allowed to determine the resonant frequencies of the metamaterial as well as an enhancement factor of the electric field as a function of the period of the metamaterial's lattice.

Studies of Magnetoresistance in GaAs:Te Crystals with Structural Disorder at Doping Limit

80%

Tarkowski T. , Słupiński T. , Karpierz K.

Acta Physica Polonica A

2011

tom 119

nr 5

726-728

Transverse magnetoresistance was studied in monocrystalline GaAs:Te doped above the equilibrium doping limit and annealed to partially deactivate donor impurities. It is shown that in a sample with partial deactivation of Te impurities, which exhibits structural fluctuations in microscale, both strong positive and some negative magnetoresistances arise, which are difficult to understand within the relaxation time approximation in degenerated homogeneous semiconductor. It is discussed that a consideration of the role of spatial fluctuations (in carrier concentration, conductivity, etc.), e.g. as proposed by Herring, allows for an understanding of positive component of magnetoresistance observed in the sample with a distinct microscopic structural disorder. With the aim to better understand the transport in GaAs:Te, a model material doped above the doping limit, we discuss both positive and negative components of measured magnetoresistance.

Structure and Energetics of Fragments of the Planar α and β Boron Sheets

80%

Gonzalez Szwacki N. , Tarkowski T. , Majewski J.

Acta Physica Polonica A

2016

tom 129

nr 1a

A-148-A-149

Large scale first principles calculations based on density functional theory and using hybrid exchange-correlation functionals have been performed in order to study the structural properties and the relative stability of fragments of the planar α and β boron sheets. Based on the considered structures, we show that, in contrast to the fragments of the α -sheet, all the fragments of the β -sheet, having more than ≈30 atoms, are fully planar regardless of their shape. We conclude that the β -sheet is the only planar boron sheet reported so far that retains planarity even if it is reduced to relatively small fragments.