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Application of Contractor Renormalization Group to the Heisenberg Zig-Zag and the Hubbard Chain

100%
Cichy K., Tomczak P.
Acta Physica Polonica A
|
2007
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vol. 111
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issue 5
773-780
EN
The contractor renormalization group method was devised in 1994 by Morningstar and Weinstein. It was primarily aimed at extracting the physics of lattice quantum field theories (like lattice quantum chromodynamics). However, it is a general method of analyzing Hamiltonian lattice systems, e.g. Ising, Heisenberg or Hubbard models. The aim of this work is to show the application of contractor renormalization group method to one-dimensional quantum systems - the Heisenberg zig-zag model and the Hubbard chain. As a test of the method, the ground state energy of these systems will be calculated.
2
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Model for the Surface Anisotropy Field Observed in Spin-Wave Resonance in (Ga,Mn)As Thin Films

100%
Puszkarski H., Tomczak P.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
508-510
EN
In this study we show why spin-wave resonance in a (Ga,Mn)As thin film may, in different conditions, meet the assumptions of either the surface inhomogeneity (SI) or the volume inhomogeneity (VI) model.
3
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A Monte Carlo Study of Critical Properties of Strongly Diluted Magnetic Semiconductor (Ga,Mn)As

81%
Tomczak P., Diep H., Jabłoński P., Puszkarski H.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
514-516
EN
Within a Monte Carlo technique we examine critical properties of diluted bulk magnetic semiconductor (Ga,Mn)As modeled by a strongly diluted ferromagnetic Heisenberg spin-5/2 system on a face centered cubic lattice. We assumed that 5% of Ga atoms is substituted by Mn atoms and the interaction between them is of the RKKY-type. The considered system is randomly quenched and a double average was performed: firstly, over the Boltzmann probability distribution and secondly - over 2048 configurations related to the quenched disorder. We estimated the critical temperature: T_{c}=97±6 K, which is in agreement with the experiment.
4
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SWR Studies of Higher-Order Surface Anisotropy Terms in (Ga,Mn)As Thin Films

81%
Puszkarski H., Tomczak P., Diep H.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
635-638
EN
We extend the theory of spin-wave resonance (SWR) by introducing a new formula representing the surface pinning parameter as a series of contributions from different anisotropies existing in (Ga,Mn)As thin films. Comparing our theory with the reported experimental studies of SWR in thin films of the ferromagnetic semiconductor (Ga,Mn)As, we find that besides the first-order cubic anisotropy, higher-order cubic anisotropies (in the second and third orders) as well as uniaxial anisotropies (perpendicular in the first and second orders, and in-plane diagonal) occur on the surface of this material. To our best knowledge this is the first report of the existence of higher-order surface anisotropy fields in (Ga,Mn)As thin films.
5
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The Ground-State of the Quantum Spin-1/2 Heisenberg Antiferromagnet on Square-Kagomé Lattice: Resonating Valence Bond Description

81%
Tomczak P., Molińska A., Richter J., Schulenburg J.
Acta Physica Polonica A
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2006
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vol. 109
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issue 6
781-787
EN
In this paper we report on some ground-state properties of the spin-1/2 Heisenberg antiferromagnet on the two-dimensional square-kagomé lattice. Finite N-spin systems were investigated with the use of the resonating valence bond method. Like in the case of spin system on kagomé lattice we find the almost flat dependence of mean singlet length on 1/N.
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