Advances in Condensed Matter Physics http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2016 , Hindawi Publishing Corporation . All rights reserved. Dosimetric UV Exposure Effect on the Optical Properties of Ag2O Doped P2O5-ZnO-CuO Glass Wed, 24 Aug 2016 15:11:15 +0000 http://www.hindawi.com/journals/acmp/2016/2360729/ Silver phosphate glass types within composition 60P2O5-30ZnO-10CuO-100000 ppm Ag2O were prepared by melt-quenching technique. The optical properties of these glass types were studied under UV exposure at different times, 0, 20, 80, 105, and 115 minutes. The optical absorbance spectra were measured in the range of wavelength from 190 to 3200 nm. The absorbance bandwidth decreases with increasing the time of UV exposure. The optical energy gap, , linear refractive index, , ratio between molar refraction, , and molar volume, , and metallization criterion () were estimated. The value of decreases from 2.132 to 1.91 eV with increasing the time of UV exposure from 0 to 115 min. Otherwise value and metallization increase with increase in the time of UV exposure. The results indicated that these glass types are promising for using an ultraviolet radiation dosimeter. K. S. Al Mugren, El Sayed Yousef, A. El-Taher, and H. Shoukry Copyright © 2016 K. S. Al Mugren et al. All rights reserved. Corrigendum to “Molecular Dynamics Simulation of Aggregates in the Dodecane/span80 System and Their Behaviour in an Electric Field” Wed, 17 Aug 2016 12:04:35 +0000 http://www.hindawi.com/journals/acmp/2016/9174604/ Madhusoodanan Mannoor, Sangmo Kang, and Yong Kweon Suh Copyright © 2016 Madhusoodanan Mannoor et al. All rights reserved. The Effect of Indium Concentration on the Structure and Properties of Zirconium Based Intermetallics: First-Principles Calculations Sun, 17 Jul 2016 13:11:47 +0000 http://www.hindawi.com/journals/acmp/2016/2536945/ The phase stability, mechanical, electronic, and thermodynamic properties of In-Zr compounds have been explored using the first-principles calculation based on density functional theory (DFT). The calculated formation enthalpies show that these compounds are all thermodynamically stable. Information on electronic structure indicates that they possess metallic characteristics and there is a common hybridization between In-p and Zr-d states near the Fermi level. Elastic properties have been taken into consideration. The calculated results on the ratio of the bulk to shear modulus (B/G) validate that InZr3 has the strongest deformation resistance. The increase of indium content results in the breakout of a linear decrease of the bulk modulus and Young’s modulus. The calculated theoretical hardness of α-In3Zr is higher than the other In-Zr compounds. Fuda Guo, Junyan Wu, Shuai Liu, and Yongzhong Zhan Copyright © 2016 Fuda Guo et al. All rights reserved. A Self-Consistent Model for Thermal Oxidation of Silicon at Low Oxide Thickness Tue, 19 Apr 2016 08:29:42 +0000 http://www.hindawi.com/journals/acmp/2016/7545632/ Thermal oxidation of silicon belongs to the most decisive steps in microelectronic fabrication because it allows creating electrically insulating areas which enclose electrically conductive devices and device areas, respectively. Deal and Grove developed the first model (DG-model) for the thermal oxidation of silicon describing the oxide thickness versus oxidation time relationship with very good agreement for oxide thicknesses of more than 23 nm. Their approach named as general relationship is the basis of many similar investigations. However, measurement results show that the DG-model does not apply to very thin oxides in the range of a few nm. Additionally, it is inherently not self-consistent. The aim of this paper is to develop a self-consistent model that is based on the continuity equation instead of Fick’s law as the DG-model is. As literature data show, the relationship between silicon oxide thickness and oxidation time is governed—down to oxide thicknesses of just a few nm—by a power-of-time law. Given by the time-independent surface concentration of oxidants at the oxide surface, Fickian diffusion seems to be neglectable for oxidant migration. The oxidant flux has been revealed to be carried by non-Fickian flux processes depending on sites being able to lodge dopants (oxidants), the so-called DOCC-sites, as well as on the dopant jump rate. Gerald Gerlach and Karl Maser Copyright © 2016 Gerald Gerlach and Karl Maser. All rights reserved. Normal Stress Differences and Yield Stresses in Attractive Particle Networks Tue, 12 Apr 2016 10:26:15 +0000 http://www.hindawi.com/journals/acmp/2016/1716598/ The nature of attractive particulate networks, yield stresses, and normal stress differences is systematically reviewed, each in terms of the relevant definitions, underlying mechanisms, and current measurement techniques. With this foundation, experimental observations of normal stress differences in some suspensions and colloidal systems are surveyed, along with constitutive models that allow for normal stress differences to arise prior to yielding. Yield stresses are a hallmark of attractive colloidal systems and vital in their processing. In contrast, little attention has been given to the role of normal stress differences in these systems. The presence or absence of normal stress differences necessarily affects the isotropy of the normal stress field through the solid particulate phase (treated as a continuum), in turn affecting estimation of yield stress. Given the importance of yield stresses in dealing with practical industrial problems, and in understanding fundamental behaviours, it is important to ensure that yield measurements can be relied upon. David I. Verrelli and Adam R. Kilcullen Copyright © 2016 David I. Verrelli and Adam R. Kilcullen. All rights reserved. Electronic Origin of Defect States in Fe-Doped LiNbO3 Ferroelectrics Wed, 23 Mar 2016 12:20:16 +0000 http://www.hindawi.com/journals/acmp/2016/2943173/ We investigate the role of Fe in the electronic structure of ferroelectric LiNbO3 by density-functional theory calculations. We show that Fe2+ on the Li site () features a displacement opposite to the direction of spontaneous polarization and acts as a trigger for the bulk photovoltaic (PV) effect. In contrast to Fe3+ on the Li site that forms the defect states (1e, a, and 2e) below the conduction band minimum, the reduction from Fe3+ to Fe2+ accompanied by a lattice relaxation markedly lowers only the state () owing to a strong orbital hybridization with Nb-4d. The state of provides the highest electron-occupied defect state in the middle of the band gap. A reduction treatment of Fe-LN is expected to increase the concentration of Fe2+ and therefore to enhance the PV effect under visible light illumination. Yuji Noguchi, Ryotaro Inoue, and Masaru Miyayama Copyright © 2016 Yuji Noguchi et al. All rights reserved. Ni-Based Ohmic Contacts to n-Type 4H-SiC: The Formation Mechanism and Thermal Stability Wed, 16 Mar 2016 09:02:14 +0000 http://www.hindawi.com/journals/acmp/2016/9273702/ The fabrication of low-resistance and thermal stable ohmic contacts is important for realization of reliable SiC devices. For the n-type SiC, Ni-based metallization is most commonly used for Schottky and ohmic contacts. Many experimental studies have been performed in order to understand the mechanism of ohmic contact formation and different models were proposed to explain the Schottky to ohmic transition for Ni/SiC contacts. In the present review, we summarize the last key results on the matter and post open questions concerning the unclear issues of ohmic contacts to n-type SiC. Analysis of the literature data and our own experimental observations have led to the conclusion that the annealing at high temperature leads to the preferential orientation of silicide at the heterointerface (0001)SiC//(013)-Ni2Si. Moreover, we may conclude that only δ-Ni2Si grains play a key role in determining electrical transport properties at the contact/SiC interface. Finally, we show that the diffusion barriers with free diffusion path microstructure can improve thermal stability of metal-SiC ohmic contacts for high-temperature electronics. A. V. Kuchuk, P. Borowicz, M. Wzorek, M. Borysiewicz, R. Ratajczak, K. Golaszewska, E. Kaminska, V. Kladko, and A. Piotrowska Copyright © 2016 A. V. Kuchuk et al. All rights reserved. Theoretical Investigation on Structural and Electronic Properties of InN Growth on Ce-Stabilized Zirconia (111) Substrates Sun, 13 Mar 2016 14:20:13 +0000 http://www.hindawi.com/journals/acmp/2016/9435387/ The structural and electronic properties of InN on Ce-stabilized zirconia (CeSZ) (111) substrates are investigated using first-principles calculations based on density functional theory with GGA + method. Surface energy calculations indicate that the structure of Ce-segregated surface is more energetically stable than that of Ce-segregation-free surface. Adsorption energies of indium and nitrogen atoms on both Ce-segregated and Ce-segregation-free CeSZ (111) surfaces at the initial growth stage have been studied. The results suggest that the first layer of InN films consists of a nitrogen layer, which leads to epitaxial relationships between InN (0001) // CeSZ (111) and InN // CeSZ . In addition, density of states (DOS) analysis revealed that the hybridization effect plays a crucial role in determining the interface structure for the growth of InN on CeSZ (111) surfaces. Furthermore, adsorption energies of indium atoms on the nitrogen layer have also been evaluated in order to investigate the lattice polarity determination for InN films. It was found that an indium atom preferentially adsorbs at the center of three nitrogen atoms stacked on the CeSZ substrate, which results in the formation of In-polarity InN. Yao Guo, Taixuan Jia, Chengbo Li, Yongsheng Niu, Shaogang Hou, and Shuanjiang Liu Copyright © 2016 Yao Guo et al. All rights reserved. Effect of In Situ Thermal Annealing on Structural, Optical, and Electrical Properties of CdS/CdTe Thin Film Solar Cells Fabricated by Pulsed Laser Deposition Mon, 29 Feb 2016 09:30:11 +0000 http://www.hindawi.com/journals/acmp/2016/8068396/ An in situ thermal annealing process (iTAP) has been introduced before the common ex situ cadmium chloride (CdCl2) annealing to improve crystal quality and morphology of the CdTe thin films after pulsed laser deposition of CdS/CdTe heterostructures. A strong correlation between the two annealing processes was observed, leading to a profound effect on the performance of CdS/CdTe thin film solar cells. Atomic force microscopy and Raman spectroscopy show that the iTAP in the optimal processing window produces considerable CdTe grain growth and improves the CdTe crystallinity, which results in significantly improved optoelectronic properties and quantum efficiency of the CdS/CdTe solar cells. A power conversion efficiency of up to 7.0% has been obtained on thin film CdS/CdTe solar cells of absorber thickness as small as 0.75 μm processed with the optimal iTAP at 450°C for 10–20 min. This result illustrates the importance of controlling microstructures of CdTe thin films and iTAP provides a viable approach to achieve such a control. Alaa Ayad Al-mebir, Paul Harrison, Ali Kadhim, Guanggen Zeng, and Judy Wu Copyright © 2016 Alaa Ayad Al-mebir et al. All rights reserved. High Dielectric Constant Study of TiO2-Polypyrrole Composites with Low Contents of Filler Prepared by In Situ Polymerization Thu, 11 Feb 2016 11:22:32 +0000 http://www.hindawi.com/journals/acmp/2016/4793434/ TiO2/polypyrrole composites with high dielectric constant have been synthesized by in situ polymerization of pyrrole in an aqueous dispersion of low concentration of TiO2, in the presence of small amount of HCl. Structural, optical, surface morphological, and thermal properties of the composites were investigated by X-ray diffractometer, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and thermogravimetric analysis, respectively. The data obtained from diffractometer and thermal gravimetric analysis confirmed the crystalline nature and thermal stability of the prepared composites. The dielectric constant of 5 wt% TiO2 increased with filler content up to 4.3 × 103 at 1 kHz and then decreased to 1.25 × 103 at 10 kHz. Khalil Ahmed, Farah Kanwal, Shahid M. Ramay, Asif Mahmood, Shahid Atiq, and Yousef S. Al-Zaghayer Copyright © 2016 Khalil Ahmed et al. All rights reserved. The First Observation of Metallic Behaviour in Nd3.5Sm0.5Ni3O8 Tue, 02 Feb 2016 08:08:46 +0000 http://www.hindawi.com/journals/acmp/2016/5808029/ In Nd3.5Sm0.5Ni3O8 which has basically the same crystal structure and the similar electrical configuration (Ni+ 3d9/Ni2+ 3d8 mix valence state) with high- cuprate, it has been found that this material shows metallic behaviour down to about 20 K by intercalation and subsequent deintercalation with sulfur. This is the first observation of the metallic state in this system. It is unclear why sulfur-intercalation and deintercalation induce the metallic state. We speculate that sulfur works as an effective getter for removing the interstitial apical oxygen which impedes the metallic conduction. However, the weak localization of carriers in the NiO2 planes still remains below 20 K and the localization may be one of the obstacles to occurrence of possible superconductivity. Akitoshi Nakata, Syunsuke Yano, Hiroki Yamamoto, Syunsuke Sakura, Yoshihide Kimishima, and Masatomo Uehara Copyright © 2016 Akitoshi Nakata et al. All rights reserved. Amphiphiles Self-Assembly: Basic Concepts and Future Perspectives of Supramolecular Approaches Tue, 29 Dec 2015 14:28:39 +0000 http://www.hindawi.com/journals/acmp/2015/151683/ Amphiphiles are synthetic or natural molecules with the ability to self-assemble into a wide variety of structures including micelles, vesicles, nanotubes, nanofibers, and lamellae. Self-assembly processes of amphiphiles have been widely used to mimic biological systems, such as assembly of lipids and proteins, while their integrated actions allow the performance of highly specific cellular functions which has paved a way for bottom-up bionanotechnology. While amphiphiles self-assembly has attracted considerable attention for decades due to their extensive applications in material science, drug and gene delivery, recent developments in nanoscience stimulated the combination of the simple approaches of amphiphile assembly with the advanced concept of supramolecular self-assembly for the development of more complex, hierarchical nanostructures. Introduction of stimulus responsive supramolecular amphiphile assembly-disassembly processes provides particularly novel approaches for impacting bionanotechnology applications. Leading examples of these novel self-assembly processes can be found, in fact, in biosystems where assemblies of different amphiphilic macrocomponents and their integrated actions allow the performance of highly specific biological functions. In this perspective, we summarize in this tutorial review the basic concept and recent research on self-assembly of traditional amphiphilic molecules (such as surfactants, amphiphile-like polymers, or lipids) and more recent concepts of supramolecular amphiphiles assembly which have become increasingly important in emerging nanotechnology. Domenico Lombardo, Mikhail A. Kiselev, Salvatore Magazù, and Pietro Calandra Copyright © 2015 Domenico Lombardo et al. All rights reserved. Synthesis and Characterization of Bifunctional α-Fe2O3-Ag Nanoparticles Mon, 14 Dec 2015 08:51:21 +0000 http://www.hindawi.com/journals/acmp/2015/320873/ The synthesis of α-Fe2O3-Ag bimetallic nanoparticles using a novel and simplified route is presented in this work. These hybrid nanoparticles were produced using a modification of the chemical reduction method by sodium borohydride (NaBH4). Fe(III) chloride hexahydrate (FeCl3·6H2O) and silver nitrate (AgNO3) as precursors were employed. Particles with semispherical morphology and dumbbell configuration were observed. High-resolution transmission electron microscopy (HRTEM) technique reveals the structure of the dumbbell-like α-Fe2O3-Ag nanoparticles. Some theoretical models further confirm the formation of the α-Fe2O3-Ag structures. Analysis by cyclic voltammetry reveals an interesting catalytic behavior which is associated with the combination of the individual properties of the Ag and α-Fe2O3 nanoparticles. Alvaro Ruíz-Baltazar, Simón Yobanny Reyes-López, Rodrigo Esparza, Miriam Estévez, Ángel Hernández-Martínez, Gerardo Rosas, and Ramiro Pérez Copyright © 2015 Alvaro Ruíz-Baltazar et al. All rights reserved. Nonlinear Tunneling of Surface Plasmon Polaritons in Periodic Structures Containing Left-Handed Metamaterial Layers Sun, 13 Dec 2015 07:48:54 +0000 http://www.hindawi.com/journals/acmp/2015/343864/ The transmission of surface plasmon polaritons through a one-dimensional periodic structure is considered theoretically by using the transfer matrix approach. The periodic structure is assumed to have alternate left-handed metamaterial and dielectric layers. Both transverse electric and transverse magnetic modes of surface plasmon polaritons exist in this structure. It is found that, for nonlinear wave propagation, tunneling structures are formed to transform nontransmitting frequencies into transmitting frequencies and hence transmission bistability is observed. It is further observed that the structure shows sensitivity with respect to the polarization of the electromagnetic field for this phenomenon. Munazza Zulfiqar Ali Copyright © 2015 Munazza Zulfiqar Ali. All rights reserved. Molecular Dynamics Simulation of Aggregates in the Dodecane/span80 System and Their Behaviour in an Electric Field Mon, 23 Nov 2015 09:42:29 +0000 http://www.hindawi.com/journals/acmp/2015/739458/ Molecular dynamics simulation of self-assembly of surfactant span80 molecules to form reverse micelles in nonpolar liquid dodecane is carried out. Simulations are performed using a united atom model for dodecane and a hybrid model for span80 molecules. Various physical characteristics of reverse micelle are measured, and the same are compared with available experimental results. Presence of charge carriers in the form of solvated ions in the core of reverse micelles is confirmed by the simulation. Movement of reverse micelles under the effect of uniform external electric field is also discussed. Madhusoodanan Mannoor, Sangmo Kang, and Yong Kweon Suh Copyright © 2015 Madhusoodanan Mannoor et al. All rights reserved. Analysis for the Sorption Kinetics of Ag Nanoparticles on Natural Clinoptilolite Sun, 22 Nov 2015 09:53:46 +0000 http://www.hindawi.com/journals/acmp/2015/284518/ The kinetic adsorption behavior of silver nanoparticles deposited on a natural zeolite from Oaxaca is presented. Theoretical models as Lagergren first-order, pseudo-second-order, Elovich, and intraparticle diffusion were employed and compared with experimental data obtained by atomic absorption spectrophotometry technique. Correlation factors of the order of 0.99 were observed. Analysis by transmission electron microscopy revealed that the silver nanoparticles were homogeneously distributed on the zeolite. Additionally, chemical characterization of the material was carried out through a dilution process with lithium metaborate. An average value of 9.3 in the Si/Al ratio was observed and related to the kinetic adsorption behavior of the zeolite. Alvaro Ruíz-Baltazar, Simón Yobanny Reyes-López, Oswald Tellez-Vasquez, Rodrigo Esparza, Gerardo Rosas, and Ramiro Pérez Copyright © 2015 Alvaro Ruíz-Baltazar et al. All rights reserved. Ultrasonic Studies of Emulsion Stability in the Presence of Magnetic Nanoparticles Thu, 12 Nov 2015 11:09:04 +0000 http://www.hindawi.com/journals/acmp/2015/398219/ Pickering emulsions are made of solid particle-stabilized droplets suspended in an immiscible continuous liquid phase. A magnetic emulsion can be obtained using magnetic particles. Solid magnetic nanoparticles are adsorbed strongly at the oil-water interface and are able to stabilize emulsions of oil and water. In this work emulsions stabilized by magnetite nanoparticles were obtained using high-energy ultrasound waves and a cavitation mechanism and, next, their stability in time was tested by means of acoustic waves with a low energy, without affecting the structure. An acoustic study showed high stability in time of magnetic emulsions stabilized by magnetite particles. The study also showed a strong influence of an external magnetic field, which can lead to changes of the emulsion properties. It is possible to control Pickering emulsion stability with the help of an external stimulus—a magnetic field. A. Józefczak and R. Wlazło Copyright © 2015 A. Józefczak and R. Wlazło. All rights reserved. Noise and Electrical Oscillations Generation during the Investigation of the Resistive Switching in the Yttria Stabilized Zirconia Films by Conductive Atomic Force Microscopy Thu, 29 Oct 2015 12:41:16 +0000 http://www.hindawi.com/journals/acmp/2015/104657/ The effect of resistive switching in the yttria stabilized zirconia (YSZ) thin films on Si substrates has been studied by Conductive Atomic Force Microscopy (CAFM). The resistive switching of the YSZ films from the low conductive state to the highly conductive one has been found to be associated with the increasing of the noise with broad frequency spectrum related to the redistribution of the oxygen vacancies in YSZ. The electrical oscillations in oscillation loop connected in series to the CAFM probe, the sample, and the bias source related to the excitation of the oscillation loop by the noise in the probe-to-sample contact film have been observed. The effect discovered is promising for application in the memristor devices of new generation. Oleg Gorshkov, Dmitry Filatov, Dmitry Antonov, and Ivan Antonov Copyright © 2015 Oleg Gorshkov et al. All rights reserved. A Process for Modelling Diffuse Scattering from Disordered Molecular Crystals, Illustrated by Application to Monoclinic 9-Chloro-10-methylanthracene Tue, 27 Oct 2015 09:08:41 +0000 http://www.hindawi.com/journals/acmp/2015/878463/ Diffuse scattering from a crystal contains valuable information about the two-body correlations (related to the nanoscale order) in the material. Despite years of development, the detailed analysis of single crystal diffuse scattering (SCDS) has yet to become part of the everyday toolbox of the structural scientist. Recent decades have seen the pair distribution function approach to diffuse scattering (in fact, total scattering) from powders become a relatively routine tool. However, analysing the detailed, complex, and often highly anisotropic three-dimensional distribution of SCDS remains valuable yet rare because there is no routine method for undertaking the analysis. At present, analysis requires significant investment of time to develop specialist expertise, which means that the analysis of diffuse scattering, which has much to offer, is not incorporated thorough studies of many compounds even though it has the potential to be a very useful adjunct to existing techniques. This article endeavours to outline in some detail how the diffuse scattering from a molecular crystal can be modelled relatively quickly and largely using existing software tools. It is hoped this will provide a template for other studies. To enable this, the entire simulation is included as deposited material. D. J. Goossens Copyright © 2015 D. J. Goossens. All rights reserved. Rare Gas Adsorption to Silver-Exchanged Zeolites Thu, 22 Oct 2015 12:31:44 +0000 http://www.hindawi.com/journals/acmp/2015/342525/ The adsorption of rare gas atoms to silver aluminosilicate has been investigated using density functional theory (DFT) with the local density approximation, generalized gradient approximation, and dispersion correction. The adsorption energies of rare gas atoms to the honeycomb lattice of silver aluminosilicate were calculated, and the results are discussed. The relationship between the electric charge density distribution and the adsorption energy is discussed. It indicates that the xenon atom has the most electrons to affect the van der Waals dispersion, so it has the highest minimum charge density, strongest polarization, most spacious spherical scope, and most favorable adsorption on silver zeolites. Qian Wang, Shulong Wen, Fanhua Hao, Zheng Huang, and Shuming Peng Copyright © 2015 Qian Wang et al. All rights reserved. Influence of Electric Field in the Adsorption of Atomic Hydrogen on Graphene Thu, 22 Oct 2015 08:28:20 +0000 http://www.hindawi.com/journals/acmp/2015/847804/ The influence of external electric field (EF) in the adsorption of atomic hydrogen on graphene (H/G) was studied by means of electronic structure calculations based on spin-polarized density functional theory with generalized gradient approximation (GGA). The changes in atomic hydrogen physisorption-chemisorption on graphene owed to EF (which ranged between −1.25 V/Å and 0.75 V/Å) were determined. Analysis of the electronic charge density for an H/G system explained the EF influences on the adsorption properties (analyzing changes in electronic charge density for H/G system). A decrease of more than 100% in the chemisorption barrier for an EF of −1.25 V/Å was found. The changes in the electronic charge density confirm the possibility of manipulating the physical-chemical adsorption of hydrogen on graphene by applying electric fields. C. Cab, R. Medina-Esquivel, C. Acosta, J. Mendez-Gamboa, F. Peñuñuri, and A. Tapia Copyright © 2015 C. Cab et al. All rights reserved. Precipitation Behavior and Magnetic Properties of Cu-Fe-Co Alloys Containing Nanogranular Ferromagnetic-Element Particles Tue, 20 Oct 2015 12:00:18 +0000 http://www.hindawi.com/journals/acmp/2015/865695/ This work investigates the evolution of microstructures and magnetic properties during isothermal annealing of Cu-Fe-Co alloys, using electron microscopy and superconducting quantum interference device (SQUID) magnetometry. Small coherent granular precipitates composed of iron and cobalt formed in the copper matrix in the early stage of precipitation. As annealing proceeded, the precipitates lost coherency to the matrix after reaching a size of 15–20 nm and twin-like structures were consecutively introduced in the particles. The SQUID measurements revealed that the magnetic properties of the specimens correlated with the microstructural evolution. The coercive force initially increased with annealing time but decreased after reaching a peak. Lorentz Microscopy suggested that the initial large increase of magnetization was invoked by a structural transition from fcc to B2 in the precipitates. N. Wada, K. Kuwada, J. S. Kim, M. Takeguchi, and M. Takeda Copyright © 2015 N. Wada et al. All rights reserved. Superconductivity, Antiferromagnetism, and Kinetic Correlation in Strongly Correlated Electron Systems Tue, 13 Oct 2015 16:42:52 +0000 http://www.hindawi.com/journals/acmp/2015/141263/ We investigate the ground state of two-dimensional Hubbard model on the basis of the variational Monte Carlo method. We use wave functions that include kinetic correlation and doublon-holon correlation beyond the Gutzwiller ansatz. It is still not clear whether the Hubbard model accounts for high-temperature superconductivity. The antiferromagnetic correlation plays a key role in the study of pairing mechanism because the superconductive phase exists usually close to the antiferromagnetic phase. We investigate the stability of the antiferromagnetic state when holes are doped as a function of the Coulomb repulsion . We show that the antiferromagnetic correlation is suppressed as is increased exceeding the bandwidth. High-temperature superconductivity is possible in this region with enhanced antiferromagnetic spin fluctuation and pairing interaction. Takashi Yanagisawa Copyright © 2015 Takashi Yanagisawa. All rights reserved. The Electronic Structure of Short Carbon Nanotubes: The Effects of Correlation Mon, 12 Oct 2015 07:35:37 +0000 http://www.hindawi.com/journals/acmp/2015/475890/ This paper presents a tight binding and ab initio study of finite zig-zag nanotubes of various diameters and lengths. The vertical energy spectra of such nanotubes are presented, as well as their spin multiplicities. The calculations performed using the tight binding approach show the existence of quasi-degenerate orbitals located around the Fermi level, thus suggesting the importance of high-quality ab initio methods, capable of a correct description of the nondynamical correlation. Such approaches (Complete Active Space SCF and Multireference Perturbation Theory calculations) were used in order to get accurate ground and nearest excited-state energies, along with the corresponding spin multiplicities. Vijay Gopal Chilkuri, Stefano Evangelisti, Thierry Leininger, and Antonio Monari Copyright © 2015 Vijay Gopal Chilkuri et al. All rights reserved. Recent Approaches for Broadening the Spectral Bandwidth in Resonant Cavity Optoelectronic Devices Wed, 07 Oct 2015 13:40:32 +0000 http://www.hindawi.com/journals/acmp/2015/605170/ Resonant cavity optoelectronic devices, such as vertical cavity surface emitting lasers (VCSELs), resonant cavity enhanced photodetectors (RCEPDs), and electroabsorption modulators (EAMs), show improved performance over their predecessors by placing the active device structure inside a resonant cavity. The effect of the optical cavity, which allows wavelength selectivity and enhancement of the optical field due to resonance, allows the devices to be made thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. However, the narrow spectral bandwidth significantly reduces operating tolerances, which leads to severe problems in applications such as optical communication, imaging, and biosensing. Recently, in order to overcome such drawbacks and/or to accomplish multiple functionalities, several approaches for broadening the spectral bandwidth in resonant cavity optoelectronic devices have been extensively studied. This paper reviews the recent progress in techniques for wide spectral bandwidth that include a coupled microcavity, asymmetric tandem quantum wells, and high index contrast distributed Bragg-reflectors. This review will describe design guidelines for specific devices together with experimental considerations in practical applications. Gun Wu Ju, Byung Hoon Na, Yong-Hwa Park, Young Min Song, and Yong Tak Lee Copyright © 2015 Gun Wu Ju et al. All rights reserved. Electrical Switching in Thin Film Structures Based on Transition Metal Oxides Mon, 05 Oct 2015 09:23:13 +0000 http://www.hindawi.com/journals/acmp/2015/654840/ Electrical switching, manifesting itself in the nonlinear current-voltage characteristics with S- and N-type NDR (negative differential resistance), is inherent in a variety of materials, in particular, transition metal oxides. Although this phenomenon has been known for a long time, recent suggestions to use oxide-based switching elements as neuristor synapses and relaxation-oscillation circuit components have resumed the interest in this area. In the present review, we describe the experimental facts and theoretical models, mainly on the basis of the Mott transition in vanadium dioxide as a model object, of the switching effect with special emphasis on the emerging applied potentialities for oxide electronics. A. Pergament, G. Stefanovich, V. Malinenko, and A. Velichko Copyright © 2015 A. Pergament et al. All rights reserved. Theoretical Approach to the Gauge Invariant Linear Response Theories for Ultracold Fermi Gases with Pseudogap Thu, 01 Oct 2015 13:36:24 +0000 http://www.hindawi.com/journals/acmp/2015/582734/ Recent experimental progress allows for exploring some important physical quantities of ultracold Fermi gases, such as the compressibility, spin susceptibility, viscosity, optical conductivity, and spin diffusivity. Theoretically, these quantities can be evaluated from suitable linear response theories. For BCS superfluid, it has been found that the gauge invariant linear response theories can be fully consistent with some stringent consistency constraints. When the theory is generalized to stronger than BCS regime, one may meet serious difficulties to satisfy the gauge invariance conditions. In this paper, we try to construct density and spin linear response theories which are formally gauge invariant for a Fermi gas undergoing BCS-Bose-Einstein Condensation (BEC) crossover, especially below the superfluid transition temperature . We adapt a particular -matrix approach which is close to the formalism to incorporate noncondensed pairing in the normal state. We explicitly show that the fundamental constraints imposed by the Ward identities and -limit Ward identity are indeed satisfied. Hao Guo and Yan He Copyright © 2015 Hao Guo and Yan He. All rights reserved. The Correlation between the Energy Gap and the Pseudogap Temperature in Cuprates: The YCBCZO and LSHCO Case Thu, 01 Oct 2015 09:42:09 +0000 http://www.hindawi.com/journals/acmp/2015/969564/ The paper analyzes the influence of the hole density, the out-of-plane or in-plane disorder, and the isotopic oxygen mass on the zero temperature energy gap (2Δ(0)) (YCBCZO) and (LSHCO) superconductors. It has been found that the energy gap is visibly correlated with the value of the pseudogap temperature (). On the other hand, no correlation between 2Δ(0) and the critical temperature () has been found. The above results mean that the value of the dimensionless ratio can vary very strongly together with the chemical composition, while the parameter does not change significantly. In the paper, the analytical formula which binds the zero temperature energy gap and the pseudogap temperature has been also presented. R. Szczȩśniak, M. W. Jarosik, and A. M. Duda Copyright © 2015 R. Szczȩśniak et al. All rights reserved. On New Families of Integrals in Analytical Studies of Superconductors within the Conformal Transformation Method Thu, 01 Oct 2015 09:39:20 +0000 http://www.hindawi.com/journals/acmp/2015/835897/ We show that, by applying the conformal transformation method, strongly correlated superconducting systems can be discussed in terms of the Fermi liquid with a variable density of states function. Within this approach, it is possible to formulate and carry out purely analytical study based on a set of fundamental equations. After presenting the mathematical structure of the -wave superconducting gap and other quantitative characteristics of superconductors, we evaluate and discuss integrals inherent in fundamental equations describing superconducting systems. The results presented here extend the approach formulated by Abrikosov and Maki, which was restricted to the first-order expansion. A few infinite families of integrals are derived and allow us to express the fundamental equations by means of analytical formulas. They can be then exploited in order to find quantitative characteristics of superconducting systems by the method of successive approximations. We show that the results can be applied in studies of high- superconductors and other superconducting materials of the new generation. Ryszard Gonczarek, Mateusz Krzyzosiak, Adam Gonczarek, and Lucjan Jacak Copyright © 2015 Ryszard Gonczarek et al. All rights reserved. Momentum Distribution Functions in a One-Dimensional Extended Periodic Anderson Model Sun, 20 Sep 2015 11:10:49 +0000 http://www.hindawi.com/journals/acmp/2015/614017/ We study the momentum distribution of the electrons in an extended periodic Anderson model, where the interaction, , between itinerant and localized electrons is taken into account. In the symmetric half-filled model, due to the increase of the interorbital interaction, the electrons become more and more delocalized, while the itinerancy of conduction electrons decreases. Above a certain value of the electrons become again localized together with the conduction electrons. In the less than half-filled case, we observe that causes strong correlations between the electrons in the mixed valence regime. I. Hagymási, J. Sólyom, and Ö. Legeza Copyright © 2015 I. Hagymási et al. All rights reserved.