arXiv subjects

M. Pudlak

Publications and source records attributed to M. Pudlak.

18 recordsLinked to original sources

arXiv2024

Valley focusing effect in a rippled graphene superlattice

Graphene corrugations affect hybridization of $π$ and $σ$ orbitals of carbon atoms in graphene based systems. It can as well break differently the symmetry of the electron transfer integrals for different strip boundaries. Using these facts, we found that the momentum distribution of electrons in ballistically propagating beam can be selective without external electric and/or magnetic fields in the graphene strip under experimentally feasible periodic potential. Such a potential is created by means of the superlattice that consists of periodically repeated graphene elements (flat+rippled junction) with different hybridization of carbon orbits, produced by variation of the graphene surface curvature. As a result it gives rise to the valley dependent focusing effects that can be controlled by alteration of number of superlattice elements.

cond-mat.mes-hall↗

arXiv2019

Spin-dependent electron transmission across the corrugated graphene

We study various mechanisms of electron transmission across the corrugations in the graphene sheet. The spin dependence of the electron transmission probability in the rippled graphene is found. The electrons mean free path and transmission probabilities are analysed for different distributions of ripples in the graphene sheet as well. We demonstrate that the periodically repeated rippled graphene structure (the superlattice) leads to the suppression of the transmission of the ballistic electrons with one spin orientation in contrast to the other, depending on the direction of the incoming electron flow.

cond-mat.mes-hall↗

arXiv2019

Klein collimation by rippled graphene superlattice

The hybridization of $σ$ and $π$ orbitals of carbon atoms in graphene depends on the surface curvature. Considering a single junction between flat and rippled graphene subsystems, it is found an accumulation of charge in the rippled subsystem due to Klein penetration phenomenon that gives rise to n-p junction. Using this fact, we show that the momentum distribution of electrons in ballisitically propagating beam can be selective without a waveguide, or external electric, and/or magnetic fields in graphene strip under experimentally feasible one-dimensional periodic potential. Such a potential is created with the aid of superlattice that consists of periodically repeated graphene pieces withdifferent hybridizations of carbon orbits, produced by variation of the graphene surface curvature. The charge redistribution and selected transmission of electrons, caused by the superlattice, allows to control the electron focusing in the considered system by simply changing the element properties in the superlattice

cond-mat.mes-hall↗

arXiv2015

Cooperative phenomenon in a rippled graphene: Chiral spin guide

We analyze spin scattering in ballistic transport of electrons through a ripple at a normal incidence of an electron flow. The model of a ripple consists of a curved graphene surface in the form of an arc of a circle connected from the left-hand and right-hand sides to two flat graphene sheets. At certain conditions the curvature induced spin-orbit coupling creates a transparent window for incoming electrons with one spin polarization simultaneously with a backscattering of those with opposite polarization. This window is equally likely transparent for electrons with spin up and spin down that move in opposite directions. The spin filtering effect being small in one ripple becomes prominent with the increase of N consequently connected ripples that create a graphene sheet of the sinusoidal type. We present the analytical expressions for spin up (down) transmission probabilities as a function of N connected ripples.

cond-mat.mes-hall↗

arXiv2015

Calculation of the electronic structure near the tip of a graphitic nanocone

In the earlier works, the electronic structure of the graphitic nanocone for the long distance from the tip was investigated. Here, we investigate the behaviour of the given nanostructure near the tip where in our approach hybridizations of pi-orbitals need to be included. In this case, the curvature dependence of pi-orbital energy has to be imposed into the model. For this purpose, we use an approximation valid for small values of the corresponding parameters. We consider different numbers of the pentagonal defects in the tip. This localization of the electrons on the nanocone tip could be used as a real application in the electron microscopes.

cond-mat.mes-hall↗

arXiv2015

Electronic structure of disordered graphene with Green's function approach

The Green functions play a big role in the calculation of the local density of states of the carbon nanostructures. We investigate their nature for the variously oriented and disclinated graphene-like surface. Next, we investigate the case of a small perturbation generated by two heptagonal defects and from the character of the local density of states in the border sites of these defects we derive their minimal and maximal distance on the perturbed cylindrical surface. For this purpose, we transform the given surface into a chain using the Haydock recursion method. We will suppose only the nearest-neighbor interactions between the atom orbitals, in other words, the calculations suppose the short-range potential.

cond-mat.mes-hall↗

arXiv2015

Spin-orbit interaction in the graphitic nanocone

The Hamiltonian for nanocones with curvature induced spin orbit coupling have been derived. The effect of curvature induced spin orbit coupling on the electronic properties of graphitic nanocones is considered. Energy spectra for different numbers of the pentagonal defects in the tip of the nanocones are calculated. It was shown that the spin orbit interaction considerably affects the local density of states of the graphitic nanocone. This influence depends on the number of defects present at the tip of the nanocone. This property could be applied in atomic force microscopy for the construction of the probing tip.

cond-mat.mes-hall↗

arXiv2014

Spin-orbit effects in armchair carbon nanotubes: analytical results

Energy spectra and transport properties of armchair nanotubes with curvature induced spin-orbit interaction are investigated thoroughly. The spin-orbit interaction consists of two terms: the first one preserves the spin symmetry in rotating frame, while the second one breaks it. It is found that the both terms are equally important: i)at scattering on the potential step which mimics a long-range potential in the nanotubes; ii)at transport via nanotube quantum dots. It is shown that an armchair nanotube with the first spin-orbit term works as an ideal spin-filter, while the second term produces a parasitic inductance.

cond-mat.mes-hall↗

arXiv2012

Edge states of graphene bilayer strip

The electronic structure of the zig-zag bilayer strip is analyzed. The electronic spectra of the bilayer strip is computed. The dependence of the edge state band flatness on the bilayer width is found. The density of states at the Fermi level is analytically computed. It is shown that it has the singularity which depends on the width of the bilayer strip. There is also asymmetry in the density of states below and above the Fermi energy.

cond-mat.mtrl-sci↗

arXiv2011

Electronic properties of disclinated nanostructured cylinder

The electronic structure of nanocylinder without and with a small perturbation is investigated with the help of calculation of the local density of states. A continuum gauge field-theory model is used for this purpose. In this model, Dirac equation is solved on a curved surface. The local density of states is calculated from its solution. The case of 2 heptagonal defects is considered. This paper is an extension of our previous work [1] where one heptagonal and one pentagonal defects in hexagonal graphene network were compared. The metallization for the perturbed cylinder structure is found.

cond-mat.mtrl-sci↗

arXiv2011

Quantum non-equilibrium approach for fast electron transport in open systems: photosynthetic reaction centers

Creation of electron or exciton by external fields in a system with initially statistically independent unrelaxed vibrational modes leads to an initial condition term. The contribution of this term in the time convolution generalized master equation approach is studied in second order of the perturbation theory in the path integral formalism. The developed approach, applied for analysis of dynamics in the photosynthetic reaction center, exhibits the key role of the initial condition terms at the primary stage of electron transfer.

physics.bio-ph↗

arXiv2011

Electronic Structure of Disclinated Graphene in an Uniform Magnetic Field

The electronic structure in the vicinity of the 1-heptagonal and 1-pentagonal defects in the carbon graphene plane is investigated. Using a continuum gauge field-theory model the local density of states around the Fermi energy is calculated for both cases. In this model, the disclination is represented by an SO(2) gauge vortex and corresponding metric follows from the elasticity properties of the graphene membrane. To enhance the interval of energies, a self-consistent perturbation scheme is used. The Landau states are investigated and compared with the predicted values.

cond-mat.mes-hall↗

arXiv2009

Electronic properties of double-layer carbon nanotubes

The electronic spectra for double-wall zigzag and armchair nanotubes are found. The influence of nanotube curvatures on the electronic spectra is also calculated. Our finding that the outer shell is hole doped by the inner shell is in the difference between Fermi levels of individual shells which originate from the different hybridization of pi-orbital. The shift and rotation of the inner nanotube with respect to the outer nanotube are investigated. We found stable semimetal characteristics of the armchair DWNTs in regard of the shift and rotation of the inner nanotube. We predict the shift of k_F towards the bigger wave vectors with decreasing of the radius of the armchair nanotube.

cond-mat.mtrl-sci↗

arXiv2007

Electronic pathway in the photosynthetic reaction centers and some mutation of RC's

The reaction center of Chloroflexus aurantiacus and Rhodobacter sphaeroides mutation of RC`s was investigated. To describe the kinetic of the Chloroflexus aurantiacus RC's we use incoherent model of electron transfer. It was shown that the asymmetry in electronic coupling must be included to explain the experiments. For the description of Rhodobacter sphaeroides H(M182)L mutation we used partially coherent as incoherent models of electron transfer. These two models are discussed with regard to the observed electron transfer kinetics. It can be concluded that partially coherent model is more adequate. We predict some new electron pathways for describing the kinetic of RC's and some mutation.

cond-mat.soft↗

arXiv2007

Effect of symmetry on the electronic structure of spheroidal fullerenes in a weak uniform magnetic field

The effect of a weak uniform magnetic field on the electronic structure of slightly deformed fullerene molecules is studied within the continuum field-theory model. It is shown that fine structure of the electronic energy spectrum is very sensitive to the orientation of the magnetic field. In particular, we found that the magnetic field pointed in the x direction does not influence the first electronic level whereas it causes a splitting of the second energy level. This behavior differs markedly from the case of the magnetic field pointed in the z direction.

cond-mat.mtrl-sci↗

arXiv2007

Electronic structure of spheroidal fullerenes in a weak uniform magnetic field: a continuum field-theory model

The effect of a weak uniform magnetic field on the electronic structure of slightly deformed fullerene molecules is studied within the continuum field-theory model. It is shown how the existing due to spheroidal deformation fine structure of the electronic energy spectrum modifies in the presence of the magnetic field. Hyperfine splitting of the energy-levels dictated by the topological defects is also influenced by the weak external magnetic field. Exact analytical solutions for zero-energy modes are found.

cond-mat.mtrl-sci↗

arXiv2006

Low energy electronic states in spheroidal fullerenes

The field-theory model is proposed to study the electronic states near the Fermi energy in spheroidal fullerenes. The low energy electronic wavefunctions obey a two-dimensional Dirac equation on a spheroid with two kinds of gauge fluxes taken into account. The first one is so-called K spin flux which describes the exchange of two different Dirac spinors in the presence of a conical singularity. The second flux (included in a form of the Dirac monopole field) is a variant of the effective field approximation for elastic flow due to twelve disclination defects through the surface of a spheroid. We consider the case of a slightly elliptically deformed sphere which allows us to apply the perturbation scheme. It is shown exactly how a small deformation of spherical fullerenes provokes an appearance of fine structure in the electronic energy spectrum as compared to the spherical case. In particular, two quasi-zero modes in addition to the true zero mode are predicted to emerge in spheroidal fullerenes. An additional 'hyperfine' splitting of the levels (except the quasi-zero-mode states) is found.

cond-mat.mtrl-sci↗

arXiv2000

Disclination vortices in elastic media

The vortex-like solutions are studied in the framework of the gauge model of disclinations in elastic continuum. A complete set of model equations with disclination driven dislocations taken into account is considered. Within the linear approximation an exact solution for a low-angle wedge disclination is found to be independent from the coupling constants of the theory. As a result, no additional dimensional characteristics (like the core radius of the defect) are involved. The situation changes drastically for 2πvortices where two characteristic lengths, l_ϕand l_W, become of importance. The asymptotical behaviour of the solutions for both singular and nonsingular 2πvortices is studied. Forces between pairs of vortices are calculated.

patt-sol↗