Advances in Condensed Matter Physics http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. A Generalization of Electromagnetic Fluctuation-Induced Casimir Energy Wed, 25 Mar 2015 12:48:31 +0000 http://www.hindawi.com/journals/acmp/2015/198657/ Intermolecular forces responsible for adhesion and cohesion can be classified according to their origins; interactions between charges, ions, random dipole—random dipole (Keesom), random dipole—induced dipole (Debye) are due to electrostatic effects; covalent bonding, London dispersion forces between fluctuating dipoles, and Lewis acid-base interactions are due to quantum mechanical effects; pressure and osmotic forces are of entropic origin. Of all these interactions, the London dispersion interaction is universal and exists between all types of atoms as well as macroscopic objects. The dispersion force between macroscopic objects is called Casimir/van der Waals force. It results from alteration of the quantum and thermal fluctuations of the electrodynamic field due to the presence of interfaces and plays a significant role in the interaction between macroscopic objects at micrometer and nanometer length scales. This paper discusses how fluctuational electrodynamics can be used to determine the Casimir energy/pressure between planar multilayer objects. Though it is confirmation of the famous work of Dzyaloshinskii, Lifshitz, and Pitaevskii (DLP), we have solved the problem without having to use methods from quantum field theory that DLP resorted to. Because of this new approach, we have been able to clarify the contributions of propagating and evanescent waves to Casimir energy/pressure in dissipative media. Yi Zheng Copyright © 2015 Yi Zheng. All rights reserved. Quadrupole Excitations in Magnetic Susceptibility of Magnetic Nanoparticle Fe8 Tue, 24 Mar 2015 13:52:22 +0000 http://www.hindawi.com/journals/acmp/2015/854625/ Magnetic susceptibility dependence on temperatures in different magnetic fields will be discussed. Until today, to calculate magnetization and magnetic susceptibility, only dipole excitations have been considered, but, due to the symmetry of operators in Hamiltonian and also to achieve more accuracy, other multiple excitations must be taken into account too. To this end, here, both dipole and quadruple excitations are considered and then the resulting curves will be plotted in presence of different magnetic fields. Finally, seen that the graphs obtained using the multipole excitations more accurately with results taken by experimental data. Yousef Yousefi Copyright © 2015 Yousef Yousefi. All rights reserved. Low-Dimensional Semiconductor Structures for Optoelectronic Applications Tue, 24 Mar 2015 09:20:40 +0000 http://www.hindawi.com/journals/acmp/2015/156196/ Wei Lu, Hong Chen, Weida Hu, Guofeng Song, Wen Lei, and Ying Fu Copyright © 2015 Wei Lu et al. All rights reserved. Rebirth of Liquid Crystals for Sensoric Applications: Environmental and Gas Sensors Mon, 23 Mar 2015 08:39:27 +0000 http://www.hindawi.com/journals/acmp/2015/729186/ Films and droplets of liquid crystals may soon become an essential part of sensitive environmental sensors and detectors of volatile organic compounds (VOCs) in the air. In this paper a short overview of recent progress in the area of sensors based on liquid crystals is presented, along with the studies of low molar mass liquid crystals as gas sensors. The detection of VOCs in the air may rely on each of the following effects sequentially observed one after the other: (i) slight changes in orientation and order parameter of liquid crystal, (ii) formation of bubbles on the top of the liquid crystalline droplet, and (iii) complete isotropisation of the liquid crystal. These three stages can be easily monitored by a photo camera and/or optical microscopy. Detection limits corresponding to the first stage are typically lower by a factor of at least 3–6 than detection limits corresponding to isotropisation. The qualitative model taking into account the reorientation of liquid crystals is presented to account for the observed changes. P. V. Shibaev, M. Wenzlick, J. Murray, A. Tantillo, and J. Howard-Jennings Copyright © 2015 P. V. Shibaev et al. All rights reserved. Tuning Rheological Performance of Silica Concentrated Shear Thickening Fluid by Using Graphene Oxide Mon, 23 Mar 2015 08:39:14 +0000 http://www.hindawi.com/journals/acmp/2015/734250/ The addition of a small amount of graphene oxide into a traditional colloidal silica-based shear thickening fluid (STF) can lead to a significant change in viscosity, critical shear rate, storage modulus, and loss modulus of STF. This finding provides an effective way to prepare stronger and light-weight STFs. Wenchao Huang, Yanzhe Wu, Ling Qiu, Cunku Dong, Jie Ding, and Dan Li Copyright © 2015 Wenchao Huang et al. All rights reserved. Synthesis, Characterization, and Photoluminescence on the Glass Doped with AgInS2 Nanocrystals Sun, 22 Mar 2015 14:12:03 +0000 http://www.hindawi.com/journals/acmp/2015/141056/ We demonstrated a synthetic process on the glass doped with AgInS2 nanocrystals through sol-gel method under a controlled atmosphere. X-ray powder diffraction and X-ray photoelectron spectra revealed that the AgInS2 crystalline phase had formed in the glass matrix. Transmittance electron microscopy showed that these AgInS2 crystals had spherical shape and good dispersed form in the glass matrix, and their diameter distribution was mainly focused on three size regions. Furthermore, the glass doped with AgInS2 nanocrystals exhibited three photoluminescence peaks located at 1.83 eV, 2.02 eV, and 2.21 eV, which were ascribed to the introduction of AgInS2 nanocrystals in the glass. Dewu Yin, Lang Pei, Zhen Liu, Xinyu Yang, Weidong Xiang, and Xiyan Zhang Copyright © 2015 Dewu Yin et al. All rights reserved. Analysis of Low Dimensional Nanoscaled Inversion-Mode InGaAs MOSFETs for Next-Generation Electrical and Photonic Applications Sun, 22 Mar 2015 10:53:02 +0000 http://www.hindawi.com/journals/acmp/2015/423791/ The electrical characteristics of In0.53Ga0.47As MOSFET grown with Si interface passivation layer (IPL) and high gate oxide HfO2 layer have been investigated in detail. The influences of Si IPL thickness, gate oxide HfO2 thickness, the doping depth, and concentration of source and drain layer on output and transfer characteristics of the MOSFET at fixed gate or drain voltages have been individually simulated and analyzed. The determination of the above parameters is suggested based on their effect on maximum drain current, leakage current, saturated voltage, and so forth. It is found that the channel length decreases with the increase of the maximum drain current and leakage current simultaneously. Short channel effects start to appear when the channel length is less than 0.9 μm and experience sudden sharp increases which make device performance degrade and reach their operating limits when the channel length is further lessened down to 0.5 μm. The results demonstrate the usefulness of short channel simulations for designs and optimization of next-generation electrical and photonic devices. C. H. Yu, X. Y. Chen, X. D. Luo, W. W. Xu, and P. S. Liu Copyright © 2015 C. H. Yu et al. All rights reserved. Shell Thickness-Dependent Strain Distributions of Confined Au/Ag and Ag/Au Core-Shell Nanoparticles Sun, 22 Mar 2015 10:03:23 +0000 http://www.hindawi.com/journals/acmp/2015/583863/ The shell thickness-dependent strain distributions of the Au/Ag and Ag/Au core-shell nanoparticles embedded in Al2O3 matrix have been investigated by finite element method (FEM) calculations, respectively. The simulation results clearly indicate that there is a substantial strain applied on both the Au/Ag and Ag/Au core-shell nanoparticles by the Al2O3 matrix. For the Au/Ag nanoparticles, it can be found that the compressive strain existing in the shell is stronger than that on the center of core and reaches the maximum at the interface between the shell and core. In contrast, for the Ag/Au nanoparticles, the compressive strain applied on the core is much stronger than that at the interface and that in the shell. With the shell thickness increasing, both of the strains in the Au/Ag and Ag/Au nanoparticles increase as well. However, the strain gradient in the shell decreases gradually with the increasing of the shell thickness for both of Ag/Au ad Au/Ag nanoparticles. These results provide an effective method to manipulate the strain distributions of the Au/Ag and Ag/Au nanoparticles by tuning the thickness of the shell, which can further have significant influences on the microstructures and physical properties of Au/Ag and Ag/Au nanoparticles. Feng Liu, Honghua Huang, Ying Zhang, Ting Yu, Cailei Yuan, and Shuangli Ye Copyright © 2015 Feng Liu et al. All rights reserved. Modeling and Simulation of a Resonant-Cavity-Enhanced InGaAs/GaAs Quantum Dot Photodetector Sun, 22 Mar 2015 09:16:18 +0000 http://www.hindawi.com/journals/acmp/2015/847510/ We simulated and analyzed a resonant-cavity-enhancedd InGaAs/GaAs quantum dot n-i-n photodiode using Crosslight Apsys package. The resonant cavity has a distributed Bragg reflector (DBR) at one side. Comparing with the conventional photodetectors, the resonant-cavity-enhanced photodiode (RCE-PD) showed higher detection efficiency, faster response speed, and better wavelength selectivity and spatial orientation selectivity. Our simulation results also showed that when an AlAs layer is inserted into the device structure as a blocking layer, ultralow dark current can be achieved, with dark current densities 0.0034 A/cm at 0 V and 0.026 A/cm at a reverse bias of 2 V. We discussed the mechanism producing the photocurrent at various reverse bias. A high quantum efficiency of 87.9% was achieved at resonant wavelength of 1030 nm with a FWHM of about 3 nm. We also simulated InAs QD RCE-PD to compare with InGaAs QD. At last, the photocapacitance characteristic of the model has been discussed under different frequencies. W. W. Wang, F. M. Guo, and Y. Q. Li Copyright © 2015 W. W. Wang et al. All rights reserved. Modeling and Design of Graphene GaAs Junction Solar Cell Sun, 22 Mar 2015 09:02:29 +0000 http://www.hindawi.com/journals/acmp/2015/326384/ Graphene based GaAs junction solar cell is modeled and investigated by Silvaco TCAD tools. The photovoltaic behaviors have been investigated considering structure and process parameters such as substrate thickness, dependence between graphene work function and transmittance, and n-type doping concentration in GaAs. The results show that the most effective region for photo photogenerated carriers locates very close to the interface under light illumination. Comprehensive technological design for junction yields a significant improvement of power conversion efficiency from 0.772% to 2.218%. These results are in good agreement with the reported experimental work. Yawei Kuang, Yushen Liu, Yulong Ma, Jing Xu, Xifeng Yang, Xuekun Hong, and Jinfu Feng Copyright © 2015 Yawei Kuang et al. All rights reserved. Photoelectric Characteristics of Double Barrier Quantum Dots-Quantum Well Photodetector Sun, 22 Mar 2015 08:54:53 +0000 http://www.hindawi.com/journals/acmp/2015/920805/ The photodetector based on double barrier AlAs/GaAs/AlAs heterostructures and a layer self-assembled InAs quantum dots and In0.15Ga0.85As quantum well (QW) hybrid structure is demonstrated. The detection sensitivity and detection ability under weak illuminations have been proved. The dark current of the device can remain at 0.1 pA at 100 K, even lower to  A, at bias of −1.35 V. Its current responsivity can reach about  A/W when 1 pw 633 nm light power and −4 V bias are added. Meanwhile a peculiar amplitude quantum oscillation characteristic is observed in testing. A simple model is used to qualitatively describe. The results demonstrate that the InAs monolayer can effectively absorb photons and the double barrier hybrid structure with quantum dots in well can be used for low-light-level detection. M. J. Wang, F. Y. Yue, and F. M. Guo Copyright © 2015 M. J. Wang et al. All rights reserved. Determination of Temperature-Dependent Stress State in Thin AlGaN Layer of AlGaN/GaN HEMT Heterostructures by Near-Resonant Raman Scattering Sun, 22 Mar 2015 08:54:43 +0000 http://www.hindawi.com/journals/acmp/2015/918428/ The temperature-dependent stress state in the AlGaN barrier layer of AlGaN/GaN heterostructure grown on sapphire substrate was investigated by ultraviolet (UV) near-resonant Raman scattering. Strong scattering peak resulting from the A1(LO) phonon mode of AlGaN is observed under near-resonance condition, which allows for the accurate measurement of Raman shifts with temperature. The temperature-dependent stress in the AlGaN layer determined by the resonance Raman spectra is consistent with the theoretical calculation result, taking lattice mismatch and thermal mismatch into account together. This good agreement indicates that the UV near-resonant Raman scattering can be a direct and effective method to characterize the stress state in thin AlGaN barrier layer of AlGaN/GaN HEMT heterostructures. Yanli Liu, Xifeng Yang, Dunjun Chen, Hai Lu, Rong Zhang, and Youdou Zheng Copyright © 2015 Yanli Liu et al. All rights reserved. Experimental Determination of Effective Minority Carrier Lifetime in HgCdTe Photovoltaic Detectors Using Optical and Electrical Methods Sun, 22 Mar 2015 08:48:42 +0000 http://www.hindawi.com/journals/acmp/2015/482738/ This paper presents experiment measurements of minority carrier lifetime using three different methods including modified open-circuit voltage decay (PIOCVD) method, small parallel resistance (SPR) method, and pulse recovery technique (PRT) on pn junction photodiode of the HgCdTe photodetector array. The measurements are done at the temperature of operation near 77 K. A saturation constant background light and a small resistance paralleled with the photodiode are used to minimize the influence of the effect of junction capacitance and resistance on the minority carrier lifetime extraction in the PIOCVD and SPR measurements, respectively. The minority carrier lifetime obtained using the two methods is distributed from 18 to 407 ns and from 0.7 to 110 ns for the different Cd compositions. The minority carrier lifetime extracted from the traditional PRT measurement is found in the range of 4 to 20 ns for . From the results, it can be concluded that the minority carrier lifetime becomes longer with the increase of Cd composition and the pixels dimensional area. Haoyang Cui, Jialin Wang, Chaoqun Wang, Can Liu, Kaiyun Pi, Xiang Li, Yongpeng Xu, and Zhong Tang Copyright © 2015 Haoyang Cui et al. All rights reserved. Photoresponse of Long-Wavelength AlGaAs/GaAs Quantum Cascade Detectors Thu, 19 Mar 2015 14:21:09 +0000 http://www.hindawi.com/journals/acmp/2015/306912/ We study the photoresponse and photocurrents of long-wavelength infrared quantum cascade detectors (QCDs) based on AlGaAs/GaAs material system. The photocurrent spectra were measured at different temperatures from 20 K to 100 K with a low noise Fourier transforming infrared spectrometer. The main response peak appeared at 8.9 μm while four additional response peaks from 4.5 μm to 10.1 μm were observed as well. We confirmed that the photocurrent comes from phonon assisted tunneling and the multipeak behavior comes from the complicated optical transition in the quantum cascade structure. This work is valuable for the future design and optimization of QCD devices. Liang Li and Dayuan Xiong Copyright © 2015 Liang Li and Dayuan Xiong. All rights reserved. Core Microstructure and Strain State Analysis in MgB2 Wires with Different Metal Sheaths Tue, 17 Mar 2015 06:26:28 +0000 http://www.hindawi.com/journals/acmp/2015/297363/ We present a detailed analysis of the effect of the sheath materials on the microstructure and superconducting properties of MgB2 wires produced by the powder-in-tube method (PIT). We reduced commercial MgB2 powder by attrition milling in nitrogen atmosphere using tungsten carbide balls and obtained powders with grain sizes lower than 150 nm and different strain states through this process. Several Ti, stainless steel, and copper monofilamentary wires were prepared using these powders by the PIT method. We investigated different thermal treatments and mechanical paths during the processing of the wires for the enhancement of the critical currents. The superconducting properties were determined by magnetization measurements in a SQUID magnetometer. The correlation between the thermal treatments, structure, and superconducting properties is discussed. C. E. Sobrero, M. T. Malachevsky, and A. Serquis Copyright © 2015 C. E. Sobrero et al. All rights reserved. Variation of Heat Flux at Lower Frequencies of Vibration in a Vibrated Granular Bed Thu, 12 Mar 2015 14:08:55 +0000 http://www.hindawi.com/journals/acmp/2015/598354/ Granular flows in vibrated bed exhibit various physical phenomena primarily driven by vibrating base. As the vibrating surface is the only source of energy in an otherwise dissipative flow, most of the theoretical models relate the steady state energy input to the RMS velocity of vibration. Here variation of heat flux is studied at varying frequency of vibration while keeping the RMS vibration velocity and the cell loading constant. Using single particle analysis and MD simulations, an extended version of grain-base collision is observed resulting in the reduction of heat flux at lower frequencies (<50 Hz) of vibration. The presented findings are important as most experimental studies are reported at these frequencies of excitation. Nadeem Ahmed Sheikh, Shehryar Manzoor, and Muzaffar Ali Copyright © 2015 Nadeem Ahmed Sheikh et al. All rights reserved. Analysis of Switchable Spin Torque Oscillator for Microwave Assisted Magnetic Recording Tue, 10 Mar 2015 15:24:09 +0000 http://www.hindawi.com/journals/acmp/2015/457456/ A switchable spin torque oscillator (STO) with a negative magnetic anisotropy oscillation layer for microwave assisted magnetic recording is analyzed theoretically and numerically. The equations for finding the STO frequency and oscillation angle are derived from Landau-Lifshitz-Gilbert (LLG) equation with the spin torque term in spherical coordinates. The theoretical analysis shows that the STO oscillating frequency remains the same and oscillation direction reverses after the switching of the magnetization of the spin polarization layer under applied alternative magnetic field. Numerical analysis based on the derived equations shows that the oscillation angle increases with the increase of the negative anisotropy energy density (absolute value) but decreases with the increase of spin current, the polarization of conduction electrons, the saturation magnetization, and the total applied magnetic field in the direction. The STO frequency increases with the increase of spin current, the polarization of conduction electrons, and the negative anisotropy energy density (absolute value) but decreases with the increase of the saturation magnetization and the total applied magnetic field in the direction. Mingsheng Zhang, Tiejun Zhou, and Zhimin Yuan Copyright © 2015 Mingsheng Zhang et al. All rights reserved. Reduction of Lattice Thermal Conductivity in PbTe Induced by Artificially Generated Pores Sun, 08 Mar 2015 07:12:11 +0000 http://www.hindawi.com/journals/acmp/2015/496739/ Highly dense pore structure was generated by simple sequential routes using NaCl and PVA as porogens in conventional PbTe thermoelectric materials, and the effect of pores on thermal transport properties was investigated. Compared with the pristine PbTe, the lattice thermal conductivity values of pore-generated PbTe polycrystalline bulks were significantly reduced due to the enhanced phonon scattering by mismatched phonon modes in the presence of pores (200 nm–2 μm) in the PbTe matrix. We obtained extremely low lattice thermal conductivity (~0.56 W m−1 K−1 at 773 K) in pore-embedded PbTe bulk after sonication for the elimination of NaCl residue. Jae-Yeol Hwang, Eun Sung Kim, Syed Waqar Hasan, Soon-Mok Choi, Kyu Hyoung Lee, and Sung Wng Kim Copyright © 2015 Jae-Yeol Hwang et al. All rights reserved. Half-Metallic Ferromagnetism in Chalcopyrite (AlGaMn)P2 Alloys Tue, 03 Mar 2015 14:00:00 +0000 http://www.hindawi.com/journals/acmp/2015/706957/ We studied the electronic and magnetic properties of (Al1−yMny)GaP2 (Ga-rich) and Al(Ga1−yMny)P2 (Al-rich) with y = 0.03125, 0.0625, 0.09375, and 0.125 by using the first-principles calculations. The ferromagnetic Mn-doped AlGaP2 chalcopyrite is the most energetically favorable one. The spin polarized Al(GaMn)P2 state (Al-rich system) is more stable than spin polarized (AlMn)GaP2 state (Ga-rich) with the magnetic moment of 3.8 /Mn. The Mn-doped AlGaP2 yields strong half-metallic ground states. The states of host Al, Ga, or P atoms at the Fermi level are mainly a P-3p character, which mediates a strong interaction between the Mn-3d and P-3p states. Byung-Sub Kang, Kwang-Pyo Chae, and Haeng-Ki Lee Copyright © 2015 Byung-Sub Kang et al. All rights reserved. The Chemistry of Bioconjugation in Nanoparticles-Based Drug Delivery System Sat, 28 Feb 2015 14:01:56 +0000 http://www.hindawi.com/journals/acmp/2015/198175/ Nanomedicine is, generally, the application of nanotechnology to medicine. The term nanomedicine includes monitoring, construction of novel drug delivery systems, and any possible future applications of nanotechnology and nanovaccinology. In this review, the most important ligand-nanocarrier and drug-nanocarrier bioconjugations are described. The detailed characterizations of covalently formed bonds between targeted ligand and nanocarrier, including amide, thioether, disulfide, acetyl-hydrazone and polycyclic groups, are described. Also, the coupling of small elements and heteroatoms in the form of R-X-R the “click chemistry” groups is shown. Physical adsorption and chemical bonding of drug to nanocarrier surface involving drug on the internal or external surfaces of nanocarriers are described throughout possibility of the formation of the above-mentioned functionalities. Moreover, the most popular nanostructures (liposomes, micelles, polymeric nanoparticles, dendrimers, carbon nanotubes, and nanohorns) are characterized as nanocarriers. Building of modern drug carrier is a new method which could be effectively applied in targeted anticancer therapy. Karolina Werengowska-Ciećwierz, Marek Wiśniewski, Artur P. Terzyk, and Sylwester Furmaniak Copyright © 2015 Karolina Werengowska-Ciećwierz et al. All rights reserved. Entanglement Area Law in Disordered Free Fermion Anderson Model in One, Two, and Three Dimensions Sat, 28 Feb 2015 07:59:31 +0000 http://www.hindawi.com/journals/acmp/2015/397630/ We calculate numerically the entanglement entropy of free fermion ground states in one-, two-, and three-dimensional Anderson models and find that it obeys the area law as long as the linear size of the subsystem is sufficiently larger than the mean free path. This result holds in the metallic phase of the three-dimensional Anderson model, where the mean free path is finite although the localization length is infinite. Relation between the present results and earlier ones on area law violation in special one-dimensional models that support metallic phases is discussed. Mohammad Pouranvari, Yuhui Zhang, and Kun Yang Copyright © 2015 Mohammad Pouranvari et al. All rights reserved. The THz Spectrum of Density Fluctuations of Water: The Viscoelastic Regime Thu, 26 Feb 2015 10:55:54 +0000 http://www.hindawi.com/journals/acmp/2015/137435/ Relevant advances in the knowledge of the water dynamics at mesoscopic scales are reviewed, while mainly focusing on the contribution provided by high resolution inelastic X-ray scattering (IXS). In particular it is discussed how the use of IXS has improved our understanding of viscoelastic properties of water at THz frequencies. This specifically involves some solid-like features such as the onset of shear wave propagation, a sound velocity surprisingly similar to the one of ice, and an anomalously low sound absorption coefficient. All these properties can be explained by assuming the coupling of THz density fluctuations with a structural relaxation process connected to the breaking and forming of hydrogen bonds (HBs). This review also includes more recent IXS results demonstrating that, upon approaching supercritical conditions, relaxation phenomena in water gradually lose their structural character becoming essentially collisional in character. Furthermore, GHz spectroscopy results on supercooled water, suggesting the occurrence of a structural arrest, are discussed. An overview of the new opportunities offered by next generation IXS spectrometers finally concludes this review. Alessandro Cunsolo Copyright © 2015 Alessandro Cunsolo. All rights reserved. Two-Dimensional Metallicity with a Large Spin-Orbit Splitting: DFT Calculations of the Atomic, Electronic, and Spin Structures of the Au/Ge(111)- Surface Wed, 25 Feb 2015 11:39:45 +0000 http://www.hindawi.com/journals/acmp/2015/531498/ Density functional theory (DFT) is applied to study the atomic, electronic, and spin structures of the Au monolayer at the Ge(111) surface. It is found that the theoretically determined most stable atomic geometry is described by the conjugated honeycomb-chained-trimer (CHCT) model, in a very good agreement with experimental data. The calculated electronic structure of the system, being in qualitatively good agreement with the photoemission measurements, shows fingerprints of the many-body effects (self-interaction corrections) beyond the LDA or GGA approximations. The most interesting property of this surface system is the large spin splitting of its metallic surface bands and the undulating spin texture along the hexagonal Fermi contours, which highly resembles the spin texture at the Dirac state of the topological insulator Bi2Te3. These properties make this system particularly interesting from both fundamental and technological points of view. Andrzej Fleszar and Werner Hanke Copyright © 2015 Andrzej Fleszar and Werner Hanke. All rights reserved. Hysteresis in Two-Dimensional Liquid Crystal Models Mon, 23 Feb 2015 08:51:09 +0000 http://www.hindawi.com/journals/acmp/2015/834867/ We make a numerical study of hysteresis loop shapes within a generalized two-dimensional Random Anisotropy Nematic (RAN) model at zero temperature. The hysteresis loops appear on cycling a static external ordering field. Ordering in these systems is history dependent and involves interplay between the internal coupling constant , the anisotropy random field , and the ordering external field . Here the external field is represented by a traceless tensor, analogous to extension-type fields in continuum mechanics. The calculations use both a mean field approach and full lattice simulations. Our analysis suggests the existence of two qualitatively different solutions, which we denote as symmetric and symmetry breaking. For the set of parameters explored, only the symmetric solutions are stable. Both approaches yield qualitatively similar hysteresis curves, which are manifested either by single or double loops. But the quantitative differences indicate that mean field estimates are only of limited predictive value. Slavko Buček, Samo Kralj, and T. J. Sluckin Copyright © 2015 Slavko Buček et al. All rights reserved. Nonequilibrium Quantum Systems: Divergence between Global and Local Descriptions Mon, 23 Feb 2015 08:37:25 +0000 http://www.hindawi.com/journals/acmp/2015/615727/ Even photosynthesis—the most basic natural phenomenon underlying life on Earth—involves the nontrivial processing of excitations at the pico- and femtosecond scales during light-harvesting. The desire to understand such natural phenomena, as well as interpret the output from ultrafast experimental probes, creates an urgent need for accurate quantitative theories of open quantum systems. However it is unclear how best to generalize the well-established assumptions of an isolated system, particularly under nonequilibrium conditions. Here we compare two popular approaches: a description in terms of a direct product of the states of each individual system (i.e., a local approach) versus the use of new states resulting from diagonalizing the whole Hamiltonian (i.e., a global approach). The main difference lies in finding suitable operators to derive the Lindbladian and hence the master equation. We show that their equivalence fails when the system is open, in particular under the experimentally ubiquitous condition of a temperature gradient. By solving for the steady state populations and calculating the heat flux as a test observable, we uncover stark differences between the formulations. This divergence highlights the need to establish rigorous ranges of applicability for such methods in modeling nanoscale transfer phenomena—including during the light-harvesting process in photosynthesis. Pedro D. Manrique, Ferney Rodríguez, Luis Quiroga, and Neil F. Johnson Copyright © 2015 Pedro D. Manrique et al. All rights reserved. Hydrostatic Pressure and Built-In Electric Field Effects on the Donor Impurity States in Cylindrical Wurtzite GaN/AlxGa1−xN Quantum Rings Thu, 19 Feb 2015 12:47:35 +0000 http://www.hindawi.com/journals/acmp/2015/594176/ Within the framework of the effective mass approximation, the ground-state binding energy of a hydrogenic impurity is investigated in cylindrical wurtzite GaN/ strained quantum ring (QR) by means of a variational approach, considering the influence of the applied hydrostatic pressure along the QR growth direction and the strong built-in electric field (BEF) due to the piezoelectricity and spontaneous polarization. Numerical results show that the donor binding energy for a central impurity increases inchmeal firstly as the QR radial thickness decreases gradually and then begins to drop quickly. In addition, the donor binding energy is an increasing (a decreasing) function of the inner radius (height). It is also found that the donor binding energy increases almost linearly with the increment of the applied hydrostatic pressure. Moreover, we also found that impurity positions have an important influence on the donor binding energy. The physical reasons have been analyzed in detail. Guangxin Wang, Xiuzhi Duan, and Rui Zhou Copyright © 2015 Guangxin Wang et al. All rights reserved. Impact of Nanoparticles on Nematic Ordering in Square Wells Wed, 18 Feb 2015 06:19:32 +0000 http://www.hindawi.com/journals/acmp/2015/532745/ Nematic liquid crystalline structures within square wells are studied numerically using both Lebwohl-Lasher lattice semimicroscopic and the Landau-de Gennes mesoscopic approach. At lateral boundary wall strong planar anchoring is enforced. The cell thickness h along the z Cartesian coordinate is assumed to be smaller than the characteristic square well size R. Using semimicroscopic modelling we restrict to effectively two-dimensional systems which we study in terms of the tensor nematic order parameter. We consider impact of appropriate nanoparticles (NPs) on nematic configuration for cases where R becomes comparable to the biaxial order parameter correlation length. In this case a star-like order reconstruction biaxial profile could be formed in absence of NPs. We demonstrate existence of a rich variety of different nematic structures, including topological defects, which are enabled by presence of appropriate NPs. M. Slavinec, E. Klemenčič, M. Ambrožič, and M. Krašna Copyright © 2015 M. Slavinec et al. All rights reserved. Low-Temperature DC Carrier Transport in (Fe0.45Co0.45Zr0.10)x(Al2O3)1−x Nanocomposites Manufactured by Sputtering in Pure Ar Gas Atmosphere Tue, 17 Feb 2015 13:47:37 +0000 http://www.hindawi.com/journals/acmp/2015/320187/ This presented work investigates the structure and temperature relationship/dependence of the DC conductivity in the (Fe0.45Co0.45Zr0.10)x(Al2O3)1−x nanocomposites deposited in Ar atmosphere with composition ( at.%) and temperature ( K). It is shown that VRH displayed crossover from Mott-like to Shklovskii-Efros regimes which occurred at temperatures of 100–120 K. It is also noted that the observed shift of the percolation threshold to higher concentrations of metallic fraction can be attributed to the disordering of the metallic nanoparticles due to the incorporation of the residual oxygen in the vacuum chamber during the deposition procedure. Ivan A. Svito, Alexander K. Fedotov, Anis Saad, Momir Milosavljević, Julia A. Fedotova, Tomasz N. Kołtunowicz, and Paweł Żukowski Copyright © 2015 Ivan A. Svito et al. All rights reserved. High-Density Physical Random Number Generator Using Spin Signals in Multidomain Ferromagnetic Layer Mon, 16 Feb 2015 13:42:36 +0000 http://www.hindawi.com/journals/acmp/2015/251819/ A high-density random number generator (RNG) based on spin signals in a multidomain ferromagnetic layer in a magnetic tunnel junction (MTJ) is proposed and fabricated. Unlike conventional spin-based RNGs, the proposed method does not require one to control an applied current, leading to a time delay in the system. RNG demonstrations are performed at room temperature. The randomness of the bit sequences generated by the proposed RNG is verified using the FIPS 140-2 statistical test suite provided by the NIST. The test results validate the effectiveness of the proposed RNGs. Our results suggest that we can obtain high-density, ultrafast RNGs if we can achieve high integration on the chip. Sungwoo Chun, Seung-Beck Lee, Masahiko Hara, Wanjun Park, and Song-Ju Kim Copyright © 2015 Sungwoo Chun et al. All rights reserved. Controlled Nanoparticle Targeting and Nanoparticle-Driven Nematic Structural Transition Mon, 16 Feb 2015 06:25:54 +0000 http://www.hindawi.com/journals/acmp/2015/803480/ We study experimentally and theoretically controlled targeting of specific nanoparticles (NPs) to different regions within nematic liquid crystal. Using a simple mesoscopic Landau-de Gennes-type model in terms of a tensor nematic order parameter, we demonstrate a general mechanism which could be exploited for controlled targeting of NPs within a spatially nonhomogeneous nematic texture. Furthermore, we experimentally demonstrate using polarising microscopy that even a relatively low concentration of localised appropriate NPs could trigger a nematic structural transition. A simple estimate is derived to account for the observed transition. A. V. Dubtsov, S. V. Pasechnik, D. V. Shmeliova, S. Kralj, and R. Repnik Copyright © 2015 A. V. Dubtsov et al. All rights reserved.