arXiv subjects

S. Wolski

Publications and source records attributed to S. Wolski.

14 recordsLinked to original sources

arXiv2024

The controlled rotation of entanglement in altermagnets

Altermagnetism became very popular because of unique features, namely coupling between magnetic properties and momentum of itinerant electrons. The particular model of the altermagnetic system of our interest has already been studied in recent publications in a different context: Phys. Rev. B \textbf{108}, L140408 (2023). Here, we study the scattering process of an itinerant electron from the altermagnetic system on the electron localized in a quantum dot. We found a spatially inhomogeneous distribution of quantum entanglement in the post-scattering state. An interesting observation is the controlled rotation of entanglement achieved by means of spin-orbital coupling constant in altermagnetic. We also studied Reny entropy and the effect of disorder in the system leading to randomness in the spin-orbit constant. Our main finding is that due to the unique properties of an altermagnetic system, tuning the applied external magnetic field allows tailoring of the desired entangled state. Thus, the scattering process, in essence, mimics the Hadamard-CNOT Gate transformation, converting the initial disentangled state into the entangled state of Bell's state. In particular, we achieved more than 70 percent fidelity between the post-scattering and Bell's states.

cond-mat.stat-mech↗

arXiv2023

Topological insulator and quantum memory

Measurements done on the quantum systems are too specific. Contrary to their classical counterparts, quantum measurements can be invasive and destroy the state of interest. Besides, quantumness limits the accuracy of measurements done on quantum systems. Uncertainty relations define the universal accuracy limit of the quantum measurements. Relatively recently, it was discovered that quantum correlations and quantum memory might reduce the uncertainty of quantum measurements. In the present work, we study two different types of measurements done on the topological system. Namely, we discuss measurements done on the spin operators and the canonical pair of operators: momentum and coordinate. We quantify the spin operator's measurements through the entropic measures of uncertainty and exploit the concept of quantum memory. While for the momentum and coordinate operators, we exploit the improved uncertainty relations. We discovered that quantum memory reduces the uncertainties of spin measurements. On the hand, we proved that the uncertainties in the measurements of the coordinate and momentum operators depend on the value of the momentum and are substantially enhanced at small distances between itinerant and localized electrons (the large momentum limit). We note that the topological nature of the system leads to the spin-momentum locking. The momentum of the electron depends on the spin and vice versa. Therefore, we suggest the indirect measurement scheme for the momentum and coordinate operators through the spin operator. Due to the factor of quantum memory, such indirect measurements in topological insulators have smaller uncertainties rather than direct measurements.

quant-ph↗

arXiv2023

Magnetic scattering with spin-momentum locking: Single scatterers and diffraction grating

Simultaneous manipulation of charge and spin density distributions in materials is the key element required in spintronics applications. Here we study the formation of coupled spin and charge densities arising in scattering of electrons by domains of local magnetization producing a position-dependent Zeeman field in the presence of the spin-momentum locking typical for topological insulators. Analytically and numerically calculated scattering pattern is determined by the electron energy, domain magnetization, and size. The spin-momentum locking produces strong differences with respect to the spin-diagonal scattering and leads to the scattering asymmetry with nonzero mean scattering angle as determined by only two parameters characterizing the system. To extend the variety of possible patterns, we study scattering by diffraction gratings and propose to design them in modern nanostructures based on topological insulators to produce desired distributions of the charge and spin densities. These results can be useful for engineering of magnetic patterns for electron optics to control coupled charge and spin evolution.

cond-mat.mes-hall↗

arXiv2022

Random spin-orbit gates in the system of a Topological insulator and a Quantum dot

The spin-dependent scattering process in a system of topological insulator and quantum dot is studied. The unitary scattering process is viewed as a gate transformation applied to an initial state of two electrons. Due to the randomness imposed through the impurities and alloying-induced effects of band parameters, the formalism of the random unitary gates is implemented. For quantifying entanglement in the system, we explored concurrence and ensemble-averaged Rényi entropy. We found that applied external magnetic field leads to long-range entanglement on the distances much larger than the confinement length. We showed that topological features of itinerant electrons sustain the formation of robust long-distance entanglement, which survives even in the presence of a strong disorder.

cond-mat.mes-hall↗

arXiv2014

Charge and spin transport in a metal-semiconductor heterostructure with double Schottky barriers

Taking into account the available experimental results, we model the electronic properties and current-voltage characteristics of a ferromagnet-semiconductor junction. The Fe/GaAs interface is considered as a Fe/(i-GaAs)/n+-GaAs/n-GaAs multilayer structure with the Schottky barrier. We also calculate numerically the current-voltage characteristics of a double-Schottky-barrier structure Fe/GaAs/Fe, which are in agreement with available experimental data. For this structure, we have estimated the spin current in the GaAs layer, which characterizes spin injection from the ferromagnet to the semiconductor.

cond-mat.mtrl-sci↗

arXiv2009

Auxetic properties of polycrystals

Young's and shear moduli and Poisson's ratio of polycrystalline solids consisting of 2D quadratic and 3D cubic randomly oriented grains of the same size and shape is studied. Considered polycrystals are initially unstrained. It is shown that for such polycrystals the division of the mechanical stability regions into areas of various auxeticity properties is different than for monocrystalline solids. In particular the regions of complete auxeticity enlarge.

cond-mat.mtrl-sci↗

arXiv2009

2D and 3D cubic monocrystalline and polycrystalline materials: their stability and mechanical properties

We consider 2- and 3-dimensional cubic monocrystalline and polycrystalline materials. Expressions for Young's and shear moduli and Poisson's ratio are expressed in terms of eigenvalues of the stiffness tensor. Such a form is well suited for studying properties of these mechanical characteristics on sides of the stability triangles. For crystalline high-symmetry directions lines of vanishing Poisson's ratio are found. These lines demarcate regions of the stability triangle into areas of various auxeticity properties. The simplest model of polycrystalline 2D and 3D cubic materials is considered. In polycrystalline phases the region of complete auxetics is larger than for monocrystalline materials.

cond-mat.mtrl-sci↗

arXiv2007

Elastic properties of cubic crystals: Every's versus Blackman's diagram

Blackman's diagram of two dimensionless ratios of elastic constants is frequently used to correlate elastic properties of cubic crystals with interatomic bondings. Every's diagram of a different set of two dimensionless variables was used by us for classification of various properties of such crystals. We compare these two ways of characterization of elastic properties of cubic materials and consider the description of various groups of materials, e.g. simple metals, oxides, and alkali halides. With exception of intermediate valent compounds, the correlation coefficients for Every's diagrams of various groups of materials are greater than for Blackaman's diagrams, revealing the existence of a linear relationship between two dimensionless Every's variables. Alignment of elements and compounds along lines of constant Poisson's ratio $ν(<100>,\textbf{m})$, ($\textbf{m}$ arbitrary perpendicular to <100>) is observed. Division of the stability region in Blackman's diagram into region of complete auxetics, auxetics and non-auxetics is introduced. Correlations of a scaling and an acoustic anisotropy parameter are considered.

cond-mat.mtrl-sci↗

arXiv2007

On the upper limit of thermal conductivity GaN crystals

The maximal value of thermal conductivity κ_{max} of the perfect wurzite GaN crystal containing isotopes of natural abundance is estimated. Our upper limit of κ=4800 W/Km at T_{max}=32 K is smaller than calculated by Liu and Balandin κ=6000 W/Km and higher than obtained by Slack et al κ=3750 W/Km. The phenomenological dependence κ\propto T^{-1.43} obtained by Mion et al for the temperature interval 300-450 K is extended to 200-300K. For temperatures higher than T_max the best fitting of our experimental data to Callaway's formula is obtained for Grueneisen's constant equal to γ= 1.35.

cond-mat.mtrl-sci↗

arXiv2006

Auxetic properties and anisotropy of elastic material constants of 2D crystalline media

Anisotropies of Young's modulus E, the shear modulus G, and Poisson's ratio of all 2D symmetry systems are studied. Simple necessary and sufficient conditions on their elastic compliances are derived to identify if any of these crystals are completely auxetic, non-auxetic and auxetic. Particular attention is paid to 2D crystals of quadratic symmetry. All mechanically stable quadratic crystals are characterized by three parameters belonging to a prism with the stability triangle in the base. Regions in the stability triangle in which quadratic materials are completely auxetic, non-auxetic, and auxetic are established. Examples of all types of auxetic properties of crystals of oblique and rectangular symmetry are presented.

cond-mat.mtrl-sci↗

arXiv2006

Anisotropic properties of mechanical characteristics and auxeticity of cubic crystalline media

Explicit expressions for inverse of Young's modulus E, inverse of shear modulus G, and Poisson's ratio for cubic media are considered. All these characteristics of elastic media depend on three components of the compliance tensor S, and on direction cosines of mutually perpendicular vectors m and n with fourfold symmetry axes. These characteristics are studied for all mechanically stable cubic materials for vectors n belonging to the irreducible body angle subtended by three cubic high symmetry directions [001], [111], and [110]. Regions in the stability triangle of in which cubic elastic materials are completely auxetic, non-auxetic, and auxetic are established. Several intermediate-valence compounds belonging to the region of complete auxecity are indicated. The extreme properties of E^{-1}, G^{-1} and Poisson ratio established by Hayes and Shuvalov are confirmed.

cond-mat.mtrl-sci↗

arXiv2006

Fourth-rank tensors of Voigt's symmetry and elastic material constants for all systems of 2D crystals

Fourth-rank tensors of complete Voigt's symmetry, that embody the elastic properties of crystalline anisotropic substances, were constructed for all 2D crystal systems. Using them we obtained explicit expressions for inverse of Young's modulus E, inverse of shear modulus G and Poisson's ratio, which depend on components of the elastic compliances tensor S, on direction cosines of vectors n of uniaxial load and the vector m of lateral strain with crystalline symmetry axes. All 2D crystal systems are considered. Such representation yields decomposition of the above elastic characteristics to isotropic and anisotropic parts. Expressions for Poisson's coefficient are well suited for studying the property of auxeticity and anisotropy 2D crystals. Phase velocities are calculated for all 2D crystal classes.

cond-mat.mtrl-sci↗

arXiv2006

Young's and shear moduli and Poisson's ratio for elastic media of high and middle symmetry

Using bases of fourth rank tensorial bases of complete Voigt's symmetry elaborated by Walpole we obtained expressions for inverse of Young's modulus E, inverse of shear modulus G and Poisson's ratio, which depend on components of the stiffness tensor S, on direction cosines of vectors n of uniaxial load and the vector m of lateral strain with crystalline symmetry axes. Crystalline media of high and medium symmetries are considered. Such representation yields decomposition of the above elastic characteristics to isotropic and anisotropic parts. Expressions for Poisson's coefficient are well suited for studying the property of auxeticity.

cond-mat.mtrl-sci↗

arXiv2006

Heat capacity and phonon mean free path of wurtzite GaN

We report on lattice specific heat of bulk hexagonal GaN measured by the heat flow method in the temperature range 20-300 K and by the adiabatic method in the range 5-70 K. We fit the experimental data using two temperatures model. The best fit with the accuracy of 3 % was obtained for the temperature independent Debye's temperature $θ_{\rm D}=365$ {\rm K} and Einstein's temperature $θ_{\rm E}=880$ {\rm K}. We relate these temperatures to the function of density of states. Using our results for heat conduction coefficient, we established in temperature range 10-100 K the explicit dependence of the phonon mean free path on temperature $\it{l}_{\rm ph}\propto T^{-2}$. Above 100 K, there is the evidence of contribution of the Umklapp processes which limit phonon free path at high temepratures. For phonons with energy $k_{\rm B}\times 300 $ {\rm K} the mean free path is of the order 100 {\rm nm}

cond-mat.mtrl-sci↗