PMC Physics B - Latest articles

Ab-initio calculations of spin tunneling through an indirect barrier

Athanasios N Chantis, Titus Sandu and Jialei L Xu — 2008-06-06

We use a fully relativistic layer Green's functions approach to investigate spin-dependent tunneling through a symmetric indirect band gap barrier like GaAs/AlAs/GaAs heterostructure along [100] direction. The method is based on Linear Muffin Tin Orbitals and it is within the Density Functional Theory (DFT) in the Local Density Approximation (LDA). We find that the results of our ab-initio calculations are in good agreement with the predictions of our previous empirical tight binding model [Phys. Rev. B, 075313 (2006)]. In addition we show the k||-dependence of the spin polarization which we did not previously include in the model. The ab-initio calculations indicate a strong k||-dependence of the transmission and the spin polarization due to band non-parabolicity. A large window of 25–50% spin polarization was found for a barrier of 8 AlAs monolayers at k|| = 0.03 2π/a. Our calculations show clearly that the appearance of energy windows with significant spin polarization depends mostly on the location of transmission resonances and their corresponding zeros and not on the magnitude of the spin splitting in the barrier.PACS Codes: 71.70.Ej, 71.15.Mb, 71.55.Eq

Electronic structure, linear, nonlinear optical susceptibilities and birefringence of CuInX2 (X = S, Se, Te) chalcopyrite-structure compounds

Ali Hussain Reshak and S Auluck — 2008-05-19

The electronic structure, linear and nonlinear optical properties have been calculated for CuInX2 (X = S, Se, Te) chalcopyrite-structure single crystals using the state-of-the-art full potential linear augmented plane wave (FP-LAPW) method. We present results for band structure, density of states, and imaginary part of the frequency-dependent linear and nonlinear optical susceptibilities. We find that these crystals are semiconductors with direct band gaps. We have calculated the birefringence of these crystals. The birefringence is negative for CuInS2 and CuInSe2 while it is positive for CuInTe2 in agreement with the experimental data. Calculations are reported for the frequency-dependent complex second-order non-linear optical susceptibilities χ123(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@. The intra-band and inter-band contributions to the second harmonic generation increase when we replace S by Se and decrease when we replace Se by Te. We find that smaller energy band gap compounds have larger values of χ123(2)(0) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabicdaWaGaayjkaiaawMcaaaaa@34D6@ in agreement with the experimental data and previous theoretical calculations.PACS Codes: 71.15.-m, 31.15.-p

Synthesis, Infra-red, Raman, NMR and structural characterization by X-ray Diffraction of [C12H17N2]2CdCl4 and [C6H10N2]2Cd3Cl10 compounds

Iskandar Chaabane, Faouzi Hlel and Kamel Guidara — 2008-04-08

The synthesis, infra-red, Raman and NMR spectra and crystal structure of 2, 4, 4-trimethyl-4, 5-dihydro-3H-benzo [b] 14 diazepin-1-ium tetrachlorocadmate, [C12H17N2]2CdCl4 and benzene-1,2-diaminium decachlorotricadmate(II) [C6H10N2]2Cd3Cl10 are reported. The [C12H17N2]2CdCl4 compound crystallizes in the triclinic system (P1¯ MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaGqaaiab=bfaqnaanaaabaGaeGymaedaaaaa@2D26@ space group) with Z = 2 and the following unit cell dimensions: a = 9.6653(8) Å, b = 9.9081(9) Å, c = 15.3737(2) Å, α = 79.486(1)°, β = 88.610(8)° and γ = 77.550(7)°. The structure was solved by using 4439 independent reflections down to R value of 0.029. In crystal structure, the tetrachlorocadmiate anion is connected to two organic cations through N-H...Cl hydrogen bonds and van der Waals interaction as to build cation-anion-cation cohesion. The [C6H10N2]2Cd3Cl10 crystallizes in the triclinic system (P1¯ MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaGqaaiab=bfaqnaanaaabaGaeGymaedaaaaa@2D26@ space group). The unit cell dimensions are a = 6.826 (5)Å, b = 9.861 (7)Å, c = 10.344 (3)Å, α = 103.50 (1)°, β = 96.34 (4)° and γ = 109.45 (3)°, Z = 2. The final R value is 0.053 (Rw = 0.128). Its crystal structure consists of organic cations and polymeric chains of [Cd3 Cl10]4- anions running along the [011] direction, in the [C6H10N2]2Cd3Cl10 compounds hydrogen bond interactions between the inorganic chains and the organic cations, contribute to the crystal packing.PACS Codes: 61.10.Nz, 61.18.Fs, 78.30.-j

Fast and accurate simulations of transmission-line metamaterials using transmission-matrix method

Hui Feng Ma, Tie Jun Cui, Jessie Yao Chin and Qiang Cheng — 2008-04-08

Recently, two-dimensional (2D) periodically L and C loaded transmission-line (TL) networks have been applied to represent metamaterials. The commercial Agilent's Advanced Design System (ADS) is a commonly-used tool to simulate the TL metamaterials. However, it takes a lot of time to set up the TL network and perform numerical simulations using ADS, making the metamaterial analysis inefficient, especially for large-scale TL networks. In this paper, we propose transmission-matrix method (TMM) to simulate and analyze the TL-network metamaterials efficiently. Compared to the ADS commercial software, TMM provides nearly the same simulation results for the same networks. However, the model-process and simulation time has been greatly reduced. The proposed TMM can serve as an efficient tool to study the TL-network metamaterials.PACS Codes: 41.20.Jb

Zone center phonons of the orthorhombic RMnO3 (R = Pr, Eu, Tb, Dy, Ho) perovskites

HC Gupta and Upendra Tripathi — 2008-03-17

A short range force constant model (SRFCM) has been applied for the first time to investigate the phonons in RMnO3 (R = Pr, Eu, Tb, Dy, Ho) perovskites in their orthorhombic phase. The calculations with 17 stretching and bending force constants provide good agreement for the observed Raman frequencies. The infrared frequencies have been assigned for the first time.PACS Codes: 36.20.Ng, 33.20.Fb, 34.20.Cf

Optical second harmonic generation in Yttrium Aluminum Borate single crystals (theoretical simulation and experiment)

Ali H Reshak, S Auluck, A Majchrowski and IV Kityk — 2008-03-17

Experimental measurements of the second order susceptibilities for the second harmonic generation are reported for YAl3(BO3)4 (YAB) single crystals for the two principal tensor components xyz and yyy. First principle's calculation of the linear and nonlinear optical susceptibilities for Yttrium Aluminum Borate YAl3(BO3)4 (YAB) crystal have been carried out within a framework of the full-potential linear augmented plane wave (FP-LAPW) method. Our calculations show a large anisotropy of the linear and nonlinear optical susceptibilities. The observed dependences of the second order susceptibilities for the static frequency limit and for the frequency may be a consequence of different contribution of electron-phonon interactions. The imaginary parts of the second order SHG susceptibility χ123(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@, χ112(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIXaqmcqaIYaGmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B1@, χ222(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIYaGmcqaIYaGmcqaIYaGmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@, and χ213(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIYaGmcqaIXaqmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@ are evaluated. We find that the 2ω inter-band and intra-band contributions to the real and imaginary parts of χijk(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKfMBHbqedmvETj2BSbqee0evGueE0jxyaibaieYdOi=BI8qipeYdI8qiW7rqqrFfpeea0xe9LqFf0xc9q8qqaqFn0dXdHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacaWGPbGaamOAaiaadUgaaeaacaGGOaGaaGOmaiaacMcaaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@3752@ show opposite signs. The calculated second order susceptibilities are in reasonable good agreement with the experimental measurements.PACS Codes: 71.15. Mb; 71.15.-m

Influence of sintering temperature on resistivity, magnetoresistance and thermopower of La0.67Ca0.33MnO3

G Venkataiah, YK Lakshmi and PV Reddy — 2008-03-12

A systematic investigation of La0.67Ca0.33MnO3 manganites has been undertaken, mainly to understand the influence of varying crystallite size (nano meter range) on electrical resistivity, magnetic susceptibility and thermoelectric power. The materials were prepared by the sol-gel method of sintering at four different temperatures between 800–1100°C. The samples were characterized by X-ray diffraction and data were analyzed using Rietveld refinement. The metal-insulator transition temperatures (TP) are found to increase with increasing sintering temperatures, while the magnetic transition temperatures (TC) decrease.The electrical resistivity and thermoelectric power data at low temperatures (T < TP) have been analyzed by considering various scattering phenomena, while the high temperature (T > TP) data were analyzed with Mott's small polaron hopping conduction mechanisms.PACS Codes: 73.50.Lw, 75.47.Gk, 75.47.Lx

Evidence of phonon-assisted tunnelling in electrical conduction through DNA molecules

Povilas Pipinys and Antanas Kiveris — 2008-02-19

We propose a phonon-assisted tunnelling model for explanation of conductivity dependence on temperature and temperature-dependent I-V characteristics in deoxyribonucleic acid (DNA) molecules. The capability of this model for explanation of conductivity peculiarities in DNA is illustrated by comparison of the temperature dependent I-V data extracted from some articles with tunnelling rate dependences on temperature and field strength computed according to the phonon-assisted tunnelling theory.PACS Codes: 87.15.-v, 71.38.-k, 73.40.Gk

Interface coupling properties and reflection of bulk spin waves from biaxial multilayer ferromagnetic media

Sergey A Reshetnyak and Tat'yana A Homenko — 2008-02-14

The reflection coefficient of bulk spin waves from multilayer ferromagnetic structure with periodically modulated parameters of exchange interaction, uniaxial and rhombic magnetic anisotropy and saturation magnetization is calculated with a non-ideal coupling between layers. The strong dependence of spin-wave reflection coefficient on frequency, magnetic field and parameter of interfacial coupling is revealed. It allows changing the reflection intensity from 0 to 1 by changing either only external magnetic field value or frequency. The proposed model of boundary conditions gives the opportunity to take into account the quality of interfaces when studying the reflection processes of spin waves in multilayer structures.PACS Codes: 75.30.Ds, 75.50.Dd, 75.70.Cn

Microwave dielectric spectroscopy of pure and mixed aromatic ester solvents

Santiago Aparicio and Rafael Alcalde — 2008-02-12

The structure and dynamics of pure and mixed liquid aromatic esters is studied through microwave dielectric relaxation spectroscopy in the 200 MHz – 20 GHz frequency range. Methyl, ethyl, propyl and butyl benzoate were studied at 298.15 K to infer the alkylic chain length effect on solvents properties showing that the relaxational behaviour for the four esters is properly described with a single Debye type function for the considered range. Methylbenzoate behaviour was also analyzed in the 278.15 – 358.15 K temperature range to study the temperature effect on their properties. Experiments on phenyl acetate were carried out to analyze the effect of aromatic ring position on fluid structure. We have also considered the properties at 298.15 K of different methylbenzoate containing mixed fluids with n-hexane, cyclohexane, 1-chlorohexane, 1-hexanol, hexanoic acid and diisopropyl ether to study the effect of different functional groups on fluid structure upon mixing. All the binary mixtures studied are properly described using a bimodal Debye process in the whole composition range. Data are analyzed in terms of the proposed different species present in the fluids and their evolution with composition for mixtures, and with temperature and chain length for pure esters.PAC CODES: 77.22.Gm, 61.25.Em, 34.20.Gj