Uniform Phases Research Articles

Resistively detected NMR spectra of the crystal states of the two-dimensional electron gas in a quantizing magnetic field

Transport experiments on the two-dimensional electron gas (2DEG) confined into a semiconductor quantum well and subjected to a quantizing magnetic field have uncovered a rich variety of uniform and nonuniform phases such as the Laughlin liquids, the Wigner, bubble and Skyrme crystals and the quantum Hall stripe state. Optically pumped nuclear magnetic resonance (OP-NMR) has also been extremely useful in studying the magnetization and dynamics of electron solids with exotic spin textures such as the Skyrme crystal. Recently, it has been demonstrated that a related technique, resistively-detected nuclear magnetic resonance (RD-NMR), could be a good tool to study the topography of the electron solids in the fractional and integer quantum Hall regimes. In this work, we compute theoretically the RD-NMR line shapes of various crystal phases of the 2DEG and study the relation between their spin density and texture and their NMR spectra. This allows us to evaluate the ability of the RD-NMR to discriminate between the various types of crystal states.

Development of a low power Delay-Locked Loop in two 130 nm CMOS technologies

The design and measurement results of two low power DLL prototypes for applications in particle physics readout systems are presented. The DLLs were fabricated in two different 130 nm CMOS technologies, called process A and process B, giving the opportunity to compare these two CMOS processes. Both circuits generate 64 uniform clock phases and operate at similar frequency range, from 20 MHz up to 60 MHz (10 MHz – 90 MHz in process B). The period jitter of both DLLs is in the range 2.5 ps – 12.1 ps (RMS) and depends on the selected output phase. The complete DLL functionality was experimentally verified, confirming a very low and frequency scalable power consumption of around 0.7 mW at typical 40 MHz input. The DLL prototype, designed in process A, occupies 680 μm × 210 μm, while the same circuit designed in process B occupies 430 μm × 190 μm.

Anisotropic Quantum Hall Liquid States with No Translational Invariance in the Lowest Landau Level

Strongly correlated two-dimensional electron systems in a high perpendicular magnetic field have displayed remarkable new physics leading to the discovery of phenomena such as the integer and the fractional quantum Hall effect, to mention a few. Laughlin’s theoretical model and the composite fermion’s (CFs) approach provide a good description of the liquid electronic phases in the lowest Landau level (LLL) at relatively large filling factors. Other electronic phases at smaller filling factors of the LLL likely represent electronic Wigner solid states. It is believed that no other phases with intermediate order stabilize at the liquid–solid transition region. The current study deals with filling factor 1/6 in the LLL, a state which is very close to the critical filling factor where the liquid–solid transition takes place. With the assumption that the underlying signs of crystalline order are starting to appear at this transitional regime, we focus our attention and study the properties of a hybrid electronic phase that lacks translational invariance. To describe such a state, we consider a wave function that lies entirely in the LLL but, unlike a typical quantum Hall liquid phase, does not possess translational invariance. Although inspired by Laughlin’s approach, the wave function we introduce differs from Laughlin’s or CFs wave functions that describe translationally invariant uniform electronic phases. We perform quantum Monte Carlo simulations in a standard disk geometry to gain a better understanding of the properties of this wave function that may be considered as a precursor to the more conventional Wigner crystal phase.

Quantum phase transitions and Berezinskii-Kosterlitz-Thouless temperature in a two-dimensional spin-orbit-coupled Fermi gas

We study the effect of spin-orbit coupling on both the zero-temperature and non-zero temperature behavior of a two-dimensional (2D) Fermi gas. We include a generic combination of Rashba and Dresselhaus terms into the system Hamiltonian, which allows us to study both the experimentally relevant equal-Rashba-Dresselhaus (ERD) limit and the Rashba-only (RO) limit. At zero temperature, we derive the phase diagram as a function of the two-body binding energy and Zeeman field. In the ERD case, this phase diagram reveals several topologically distinct uniform superfluid phases, classified according to the nodal structure of the quasiparticle excitation energies. Furthermore, we use a momentum dependent SU(2)-rotation to transform the system into a generalized helicity basis, revealing that spin-orbit coupling induces a triplet pairing component of the order parameter. At non-zero temperature, we study the Berezinskii-Kosterlitz-Thouless (BKT) phase transition by including phase fluctuations of the order parameter up to second order. We show that the superfluid density becomes anisotropic due to the presence of spin-orbit coupling (except in the RO case). This leads both to elliptic vortices and antivortices, and to anisotropic sound velocities. The latter prove to be sensitive to quantum phase transitions between topologically distinct phases. We show further that at a fixed non-zero Zeeman field, the BKT critical temperature is increased by the presence of ERD spin-orbit coupling. Subsequently, we demonstrate that the Clogston limit becomes infinite: $T_{\rm{BKT}}$ remains non-zero at all finite values of the Zeeman field. We conclude by extending the quantum phase transition lines to non-zero temperature, using the nodal structure of the quasiparticle spectrum, thus connecting the BKT critical temperature with the zero-temperature results.

The influence of the flexoelectric effect on the orientational transitions in ferronematic liquid crystals

The influence of flexoelectric polarization induced by external electric and magnetic fields in a ferronematic liquid crystal on the orientational transitions between uniform and nonuniform phases is analyzed. The Freedericksz transition field and the saturation field as functions of ferronematic material parameters are determined. Bifurcation diagrams of orientational phases are analyzed. It is shown that the orientational transitions can be of the first or second order depending on the value of the segregation parameter of the dispersed phase.

In situ synthesized TiC–DLC nanocomposite coatings on titanium surface in acetylene ambient

TiC–DLC coatings were in situ synthesized on Ti target surface in acetylene ambient by cathodic arc evaporation. In this process, TiC–DLC composite phases were formed by chemical reaction between Ti target surface and ionized C ions. Different acetylene (C2H2) flow rate and synthetic time were designed as two independent variables to synthesize two series of coatings to study the effects of different synthetic parameters on structure of the coatings. Surface morphology, composition and structure of the coatings were investigated by SEM, EDS, XRD and Raman spectroscopy, respectively. The result showed that the structure and composition of the coatings on the titanium metal target surface could be controlled by changing the C2H2 flow rate. The uniform TiC-DLC composite phases were observed in the coatings, while both C2H2 flow rate and synthetic time could significantly affect the thickness and bonding state of the coatings.

The primary bilayer ruga-phase diagram I: Localizations in ruga evolution

It has been observed that coexistence of multiple ruga (wrinkle, crease, fold or ridge) phases hinders advancement of nano and soft materials technology to control and manufacture uniform ruga phases in bilayer material systems. In this paper, we construct the primary bilayer (PB) ruga-phase diagram which can guide manipulation of various ruga configurations in bilayer systems. The PB ruga-phase diagram is a generic phase diagram of a bilayer system composed of a thin film on a half-space substrate, both of which are represented as incompressible neo-Hookean solids. On the PB ruga-phase diagram, various phase boundaries represent bifurcation sites of ruga structures caused by lateral compression of the bilayer. We have identified eleven different ruga phases and five triple points of ruga phases on the PB ruga-phase diagram. All the ruga phases eventually evolve to a limit phase of either global crease or global fold localization, depending on the stiffness ratio of the bilayer, when compressed up to the Biot critical strain of 0.456. Another global localization–ridge localization which is principally caused by large substrate pre-stretch (or mismatch strain)–is treated in a sequel paper.

Striped ferronematic ground states in a spin-orbit-coupledS=1Bose gas

We theoretically establish the mean-field phase diagram of a homogeneous spin-$1$, spin-orbit coupled Bose gas as a function of the spin-dependent interaction parameter, the Raman coupling strength and the quadratic Zeeman shift. We find that the interplay between spin-orbit coupling and spin-dependent interactions leads to the occurrence of ferromagnetic or ferronematic phases which also break translational symmetry. For weak Raman coupling, increasing attractive spin-dependent interactions (as in $^{87}$Rb or $^7$Li) induces a transition from a uniform to a stripe XY ferromagnet (with no nematic order). For repulsive spin-dependent interactions however (as in $^{23}$Na), we find a transition from an $XY$ spin spiral phase ($<S_{z} >= 0$ and uniform total density) with uniaxial nematic order, to a biaxial ferronematic, where the total density, spin vector and nematic director oscillate in real space. We investigate the stability of these phases against the quadratic Zeeman effect, which generally tends to favor uniform phases with either ferromagnetic or nematic order but not both. We discuss the relevance of our results to ongoing experiments on spin-orbit coupled, spinor Bose gases.

Spin–singlet competition responsible for magnetization plateau associated with magnetocaloric effect in a tetrameric chain

The quantum phase transitions (QPTs) and magnetization plateau properties, together with magnetocaloric effect (MCE) of the tetrameric chain are investigated by means of Green’s function theory. We reveal the uniform, dimeric and gapped (gapless) tetrameric phases, which are explicitly confirmed by the field dependence of magnetization. The spin–singlet competition is proposed to make clear the magnetization plateaus and QPTs. Simultaneously, the QPTs and quantum critical points are identified by the dips of the isoentropes, or equivalently the sharp maxima of entropy at ultra-low temperature, as well as the local minima of specific heat and the valley–peak structure of magnetic cooling rate with its sign changed. In addition, the temperature (T) and magnetic field (h) dependence of magnetic entropy change (ΔS) exhibits prominent inverse magnetocaloric effect (IMCE), implying adiabatic magnetization can generate cooling, which follows a power law dependence of h: ΔS∼hn. The local exponent n≈2 is independent of h and T at low fields, which was observed in the antiferromagnetic materials experimentally. It is also found that the stronger the dimerization is, the larger the IMCE is, which would provide a clue to design antiferromagnetic refrigerant materials for use in magnetic cooling devices with low field controlling.

Effects of spin-orbit coupling on the Berezinskii-Kosterlitz-Thouless transition and the vortex-antivortex structure in two-dimensional Fermi gases.

We investigate the Berezinskii-Kosterlitz-Thouless (BKT) transition in a 2D Fermi gas with spin-orbit coupling (SOC), as a function of the two-body binding energy and a perpendicular Zeeman field. By including a generic form of the SOC, as a function of Rashba and Dresselhaus terms, we study the evolution between the experimentally relevant equal Rashba-Dresselhaus (ERD) case and the Rashba-only (RO) case. We show that in the ERD case, at a fixed nonzero Zeeman field, the BKT transition temperature T(BKT) is increased by the presence of SOC for all values of the binding energy. We also find a significant increase in the value of the Clogston limit compared to the case without SOC. Furthermore, we demonstrate that the superfluid density tensor becomes anisotropic (except in the RO case), leading to an anisotropic phase-fluctuation action that describes elliptic vortices and antivortices, which become circular in the RO limit. This deformation constitutes an important experimental signature for superfluidity in a 2D Fermi gas with ERD SOC. Finally, we show that the anisotropic sound velocities exhibit anomalies at low temperatures, in the vicinity of quantum phase transitions between topologically distinct uniform superfluid phases.

Effect of electric and magnetic fields on the orientation structure of a ferronematic liquid crystal

We analyze uniform orientation phases in soft ferronematics (suspensions of magnetic nanoparticles in nematic liquid crystals) induced by electric and magnetic fields. It is shown that the competition between the electric and magnetic fields can lead to various sequences of orientation transitions in a ferronematic depending on the energy of coupling between the director and magnetization. We obtain and analyze phase diagrams of these transitions. A sequence of re-entrant transitions in the orientation structure (angular phase-homeotropic phase-angular phase-planar phase) is predicted for a certain range of the coupling energies and electric field strengths.

Oil resistance and mechanical properties of polysiloxane nanocomposites prepared by in situ reaction of reactive polar monomers

ABSTRACTA series of poly(methylvinylsiloxane) elastomer (VMQ) composites with improved oil resistance were prepared by introducing uniform polar polymer phases into VMQ matrix through the in situ reaction of reactive polar monomers—hydroxyethyl methacrylate (HEMA) and hydroxypropyl methacrylate (HPMA)—during peroxide curing. Differential scanning calorimetry and Fourier transform infrared measurements demonstrated that HEMA and HPMA had high reactivity and most of the monomers participated in the in situ reaction during peroxide curing. Transmission electron microscopic images showed that the uniform nanophases with the diameters in the range of 20–50 nm formed in the VMQ vulcanizates. The generated nanophases could interact with silica to form a strong filler network in the VMQ matrix, resulting in a significant increase of the modulus at low elongation of the VMQ vulcanizates. With increasing the content of polar monomers, the tensile strength decreased slightly, the elongation at break, the hardness and the 100% modulus increased, but the 300% modulus decreased significantly due to the decrease of the crosslink density. The incorporation of HEMA or HPMA into VMQ matrix could significantly improve the oil resistance of polysiloxane elastomer, and the oil resistance of the composites containing HEMA was a little better than that of the composites containing HPMA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40983.

Sb2O3 Nanowires as Anode Material for Sodium-Ion Battery

The anodic properties of antimony trioxide (Sb2O3) nanowires were investigated as electrode material for sodium-ion battery. Sb2O3 nanowires were prepared via a mild-condition, solvothermal route based on the hydrolysis of antimony trichloride (SbCl3) in alcohol aqueous solution. The uniform morphology and crystal phases of Sb2O3 nanowires are confirmed by scanning electronic microscopy, transmission electronic microscopy, and X-ray diffraction. The electrochemical performance of Sb2O3 nanowire anodes was studied and the material exhibits a high reversible capacity of 230 mAh/g which is attributed to the reversible complex conversion–alloying reactions between antimony trioxide and sodium.

The Many Faces of Lipid Rafts

The Many Faces of Lipid Rafts

Activator-assisted electroless deposition of copper nanostructured films

This paper showed simple and effective synthesis of copper nanoparticles within controlled diameter using direct electroless deposition on glass substrates, following the sensitization and activation steps. Electroless-deposited metals, such as Cu, Co, Ni, and Ag, and their alloys had many advantages in micro- and nanotechnologies. The structural, morphological, and optical properties of copper deposits were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), and UV-Vis spectroscopy. The structural data was further analyzed using the Rietveld refinement program. Structural studies reveal that the deposited copper prefers a (111) orientation. AFM studies suggest the deposited materials form compact, uniform, and nanocrystalline phases with a high tendency to self-organize. The data show that the particle size can be controlled by controlling the activator concentration. The absorption spectra of the as-deposited copper nanoparticles reveal that the plasmonic peak broadens and exhibits a blue shift with decreasing particle size.

Topological superfluid phases of an atomic Fermi gas with in- and out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling

We analyze the effects of in- and out-of-plane Zeeman fields on the BCS-BEC evolution of a Fermi gas with equal Rashba-Dresselhaus (ERD) spin-orbit coupling (SOC). We show that the ground state of the system involves novel gapless superfluid phases that can be distinguished with respect to the topology of the momentum-space regions with zero excitation energy. For the BCS-like uniform superfluid phases with zero center-of-mass momentum, the zeros may correspond to one or two doubly-degenerate spheres, two or four spheres, two or four concave spheroids, or one or two doubly-degenerate circles, depending on the combination of Zeeman fields and SOC. Such changes in the topology signal a quantum phase transition between distinct superfluid phases, and leave their signatures on some thermodynamic quantities. We also analyze the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like nonuniform superfluid phases with finite center-of-mass momentum and obtain an even richer phase diagram.

Effect of Nd on the microstructure and mechanical properties of Mg–8Gd–5Y–2Zn–0.5Zr alloy

Microstructures and mechanical properties of the Mg–8Gd–5Y–2Zn–0.5Zr–xNd (x=0, 0.5, 1 and 2wt%) alloys in the as-cast, solid solution and as-aged conditions have been investigated. The experimental results reveal that Nd can impede the formation of LPSO phases during the solidification process and suppress the transformation of Mg5(Gd, Y, Zn) to LPSO phase at high temperature heat-treatment. Addition of 2% Nd leads to the disappearance of the LPSO phases in the as-cast alloy. After heat-treatment at 520°C for 16h, the uniform LPSO phases, which are transformed from Mg5(Gd, Y, Zn) phases and refined by the Nd, result in a higher solid solubility and greater aging effect. With increasing Nd content, the residual Nd-rich Mg5(Gd, Y, Zn) phases in the solid solution alloys gradually increase and produce an adverse effect on the mechanical properties. The alloy with the addition of 0.5% Nd shows the optimal mechanical properties in the as-aged alloys, and its ultimate tensile strength, yield strength and elongation are 308MPa, 252MPa and 5.3%, respectively.

Ergodic Interference Alignment

This paper develops a new communication strategy, ergodic interference alignment, for the K-user interference channel with time-varying fading. At any particular time, each receiver will see a superposition of the transmitted signals plus noise. The standard approach to such a scenario results in each transmitter-receiver pair achieving a rate proportional to 1/K its interference-free ergodic capacity. However, given two well-chosen time indices, the channel coefficients from interfering users can be made to exactly cancel. By adding up these two observations, each receiver can obtain its desired signal without any interference. If the channel gains have independent, uniform phases, this technique allows each user to achieve at least 1/2 its interference-free ergodic capacity at any signal-to-noise ratio. Prior interference alignment techniques were only able to attain this performance as the signal-to-noise ratio tended to infinity. Extensions are given for the case where each receiver wants a message from more than one transmitter as well as the “X channel” case (with two receivers) where each transmitter has an independent message for each receiver. Finally, it is shown how to generalize this strategy beyond Gaussian channel models. For a class of finite field interference channels, this approach yields the ergodic capacity region.

Modeling the structure of liquids and crystals using one- and two-component modified phase-field crystal models

A modified phase-field crystal model in which the free energy may be minimized by an order parameter profile having isolated bumps is investigated. The phase diagram is calculated in one and two dimensions and we locate the regions where modulated and uniform phases are formed and also regions where localized states are formed. We investigate the effectiveness of the phase-field crystal model for describing fluids and crystals with defects. We further consider a two-component model and elucidate how the structure transforms from hexagonal crystalline ordering to square ordering as the concentration changes. Our conclusion contains a discussion of possible interpretations of the order parameter field.

Digital Generation of Non-Gaussian Spiky Excitations Using Spectral Representation with Additive Phase Structure

AbstractThis paper presents a framework of the digital generation of non-Gaussian spiky excitations. This study is focused on the random spikiness, featuring large excursions with considerable energy and monotonic (nonstochastic) variations in a local time history. A first-order non-Gaussian stochastic time series model and its spectral representation are employed for the local spiky features. The stochastic model generates not only autocorrelation properties but also a unique shape of peaks formed with random spikes and monotonic variations between spikes. The Fourier representation of the stochastic model enables an effective control of the peaks and provides a filtering operation for the local feature generation in the frame of stationary stochastic process. Several spectral models with stochastic or ensemble-averaged amplitudes and four added phase functions have been developed. Thus, the phase is different from the uncorrelated uniform phases in a conventional spectral method. The essential feature o...