Electronic Topology Research Articles

Unconventional superconductivity on the triangular lattice Hubbard model

Using large-scale dynamical cluster quantum Monte Carlo simulations, we explore the unconventional superconductivity in the hole-doped Hubbard model on the triangular lattice. Due to the interplay of electronic correlations, geometric frustration, and Fermi surface topology, we find a doubly degenerate singlet pairing state at an interaction strength close to the bare bandwidth. Such an unconventional superconducting state is mediated by antiferromagnetic spin fluctuations along the $\Gamma$-$K$ direction, where the Fermi surface is nested. An exact decomposition of the irreducible particle-particle vertex further confirms the dominant component of the effective pairing interaction comes from the spin channel. Our findings provide support for chiral $d +i d$ superconductivity in water-intercalated sodium cobaltates Na$_{x}$CoO$_{2} \cdot y$H$_{2}$O, as well as insight into the superconducting phases of the organic compounds $\kappa$-(ET)$_{2}$X and Pd(dmit)$_{2}$.

Multiferroic behavior in elemental selenium below 40 K: effect of electronic topology.

The quasi-one-dimensional, chiral crystal structure of Selenium has fascinating implications: we report simultaneous magnetic and ferroelectric order in single crystalline Se microtubes below ≈40 K. This is accompanied by a structural transition involving a partial fragmentation of the infinite chains without losing overall crystalline order. Raman spectral data indicate a coupling of magnons with phonons and electric field, while the dielectric constant shows a strong dependence on magnetic field. Our first-principles theoretical analysis reveals that this unexpected multiferroic behavior originates from Selenium being a weak topological insulator. It thus exhibits stable electronic states at its surface, and magnetism emerges from their spin polarization. Consequently, the broken two-fold rotational symmetry permits switchable polarization along its helical axis. We explain the observed magnetoelectric couplings using a Landau theory based on the coupling of phonons with spin and electric field. Our work opens up a new class of topological surface-multiferroics with chiral bulk structure.

DFIG Sliding Mode Control Driven by Wind Turbine with Using a SVM Inverter for Improve the Quality of Energy Injected into the Electrical Grid

This paper presents a simulation study of Doubly Fed Induction Generator (DFIG) controlled by sliding mode control (SMC) applied to achieve control of active and reactive powers exchanged between the stator of the DFIG and the grid. In this paper, a variable speed wind turbine is considered with DFIG and dierent power electronic converter topologies: (i) Carried based Pulse Width Modulation (PWM), (ii) Space Vector Modulation (SVM). To improve the quality of energy injected into the electrical grid, we propose SVM technique which allows the minimizing of harmonics stator current and wide linear modu- lation range. The feasibility and eectiveness of the method is demonstrated by simulation results. The obtained results showed that, the proposed SMC with SVM inverter have stator and rotor current with low harmonic distortion and low active and reactive powers ripples than PWM inverter.

Theoretical studies of electronic structure and structural properties of anhydrous alkali metal oxalates

The results of first principles calculations of band structure, density of states, and electron density topology of alkali metal oxalates are presented. The calculations have been carried out with WIEN2k ab initio program, using highly precise full potential linearized augmented plane wave method within density functional theory formalism. Calculated total electron density has been used in calculations of its topological properties (according to Bader’s quantum theory of atoms in molecules formalism) and Cioslowski and Mixon’s topological bond orders. The obtained results show important similarities between electronic structure and electron density topology for all analyzed structures with electronic structure close to Fermi energy typical for ionic compounds and bonding which is mainly covalent within the oxalate anion (with partly ionic character of carbon–oxygen bonds) and strongly ionic between oxalate anion and cationic sublattice. These results have been used as a basis for theoretical analysis of thermal decomposition process described in detail in part II of this paper (where also the results of additional calculations of atomic and bond valences, bond strengths and strains are presented).

Sharp Raman Anomalies and Broken Adiabaticity at a Pressure Induced Transition from Band to Topological Insulator inSb2Se3

The nontrivial electronic topology of a topological insulator is thus far known to display signatures in a robust metallic state at the surface. Here, we establish vibrational anomalies in Raman spectra of the bulk that signify changes in electronic topology: an E(g)(2) phonon softens unusually and its linewidth exhibits an asymmetric peak at the pressure induced electronic topological transition (ETT) in Sb(2)Se(3) crystal. Our first-principles calculations confirm the electronic transition from band to topological insulating state with reversal of parity of electronic bands passing through a metallic state at the ETT, but do not capture the phonon anomalies which involve breakdown of adiabatic approximation due to strongly coupled dynamics of phonons and electrons. Treating this within a four-band model of topological insulators, we elucidate how nonadiabatic renormalization of phonons constitutes readily measurable bulk signatures of an ETT, which will facilitate efforts to develop topological insulators by modifying a band insulator.

Resonant inverter with resonance frequency tracking for DBD plasma reactor supply

This document gives an overview of a power supply construction suitable for dielectric barrier discharge (DBD) reactor excitation. The influence of temperature and voltage change on DBD reactor parameters is discussed. A power electronic supply system topology allowing for continuous resonant frequency tracking is proposed together with simulation and test stand results of operation. An additional feature of proposed topology is the output peak to peak voltage control.

Tunable topological electronic structures in Sb(111) bilayers: A first-principles study

Electronic structures and band topology of a single Sb(111) bilayer in the buckled honeycomb configuration are investigated using first-principles calculations. A nontrivial topological insulating phase can be induced by tensile strain, indicating the possibility of realizing the quantum spin Hall state for Sb thin films on suitable substrates. The presence of buckling provides an advantage in controlling the band gap through an out-of-plane external electric field, making a topological phase transition with six spin-polarized Dirac cones at the critical point. With a tunable gap and reversible spin polarization, Sb thin films are promising candidates for spintronic applications.

A simple electrotopological index for quantitative structure-activity relationship correlation of physical properties with biomolecular activities

Quantitative structure-activity relationship (QSAR) studies constitute a process by which the physicochemical properties of a set of chemical structures are quantitatively correlated with a measurable, such as the concentration of a substance required to give a certain therapeutic drug response. 2D-QSAR studies start with 10–20 analogues, ranging from biologically active to inactive; each analogue, regardless of bioactivity, is described by a series of descriptors. To further broaden the practical utility of these simple descriptors we have sought to identify hybrid indices which are trivial to calculate but which capture data from at least two categories of descriptors. An electrotopological descriptor, termed ET\(_\mathrm{Z}\), which combines electronic information and molecular topology, has been devised and validated against a set of 25 anticonvulsant hydantoin molecules. This ET\(_\mathrm{Z}\) is based solely on atomic connectivity information obtained from the graph without explicit input from molecular geometry.

Crystallographic Study of the TiO<sub>2</sub> Obtained by Different Synthesis Methods

In this work, the crystal structure of titanium dioxide was studied, and the effect of the different synthesis routes on the microstructure and morphology of the nanostructures was analyzed. Samples characterization was carried out by X-ray diffraction by powders (XRD) to determine the different crystalline phases contented in the samples and using scanning electron microscopy (SEM), the morphology and topology of all samples were studied. XRD results were analyzed through Eva provided by Bruker to determine the average crystallite size. The results portrayed here showed that all the synthesis process produced anatase nanostructures with an average crystallite size smaller than 27 nm. Synthesized powders presented similar morphologies in all cases and they were homogeneous in their chemical composition.

A Review of Fabrication Options and Power Electronics for Flapping-Wing Robotic Insects

Flapping-wing robotic insects are novel micro air vehicles (MAVs) inspired from biological insects in order to achieve a small size, high manoeuvrability and super remote ability. Such MAVs are centimetre scale flying robots with a number of applications, including exploration, environmental monitoring, rescue and reconnaissance. Due to the strict weight and power requirements of MAVs, the power electronics topologies need to be considered seriously. This paper describes state of the art power electronics topologies suitable for driving fl This -wing robotic insects. Comparisons are made in the resulting configurations of MAVs across several key metrics to estimate their performance. Discussion on the effect of performance gains in various power electronic topologies are abridged and presented.

Front-End Electronic Circuit Topology Analysis for Model-Driven Classification and Monitoring of Appliance Loads in Smart Buildings

This paper presents a nonintrusive appliance load monitoring (NILM) strategy for energy management systems in smart buildings. Compared to purely data-driven methods, this paper introduces a prior-knowledge-based model-driven framework. The prior-knowledge includes front-end power supply circuit identification, electrical operating principle, and customer usage. The focus of this paper is on a comprehensive study on front-end power supply circuit topologies and on the commercial power supply market. The former forms the basis of the proposed hierarchical taxonomy from the power electronics' point of view, and the latter study guarantees that the proposed taxonomy represents the majority of appliance loads in the real world. Under the proposed taxonomy, the advantage of the model-driven hierarchical feature extraction is discussed, and initial analysis shows that optimized features can be obtained from this method, which drives a much simpler AND more feasible solution in differentiating the subtle differences between similar loads.

SuperNEMO – the next generation double beta decay experiment

The SuperNEMO experiment is being designed to search for neutrinoless double beta decay to test if neutrinos are Majorana particles. The unique experimental technique follows that of the currently running NEMO 3 experiment, which successfully combines tracking and calorimetry to measure the topology and energy of the final state electrons. SuperNEMO will employ about 100 kg of 82Se to reach sensitivity to a half-life time of about 2×1026 years, which corresponds to Majorana neutrino masses of about 50 meV, and depends on the calculated value of the nuclear matrix element. The construction of the demonstrator module with 5 kg of 82Se is about to begin and, if successful, will be followed by 19 more of similar modules.

Current eigenmodes and dephasing in nanoscopic quantum networks

Using the nonequilibrium Keldysh Green's function formalism, we show that the nonequilibrium charge transport in nanoscopic quantum networks takes place via current eigenmodes that possess characteristic spatial patterns. We identify the microscopic relation between the current patterns and the network's electronic structure and topology and demonstrate that these patterns can be selected via gating or constrictions, providing new venues for manipulating charge transport at the nanoscale. Finally, decreasing the dephasing time leads to a smooth evolution of the current patterns from those of a ballistic quantum network to those of a classical resistor network.

Trends in structural, electronic properties and Fermi surface topology of 15 tetragonal ThCr2Si2-type phases AFe2Ch2, where A = Li, Na, K, Rb, and Cs; Ch = S, Se, and Te, as parent systems of new ternary iron–chalcogenide superconductors

By means of the first principles FLAPW-GGA approach, a systematic study of the structural and electronic properties of full series of 15 synthesized and hypothetical tetragonal ThCr2Si2-type phases in the system A–Fe–Ch, where A=Li, Na, K, Rb, and Cs; Ch=S, Se, and Te, was performed. We find that for the tuning of the structural parameters of conducting [Fe2Ch2] blocks the replacements of Ch2− ions will be most effective, whereas for the tuning of the inter-blocks separation [Fe2Ch2]–[Fe2Ch2] the replacements of the alkaline ions seem more useful. The trends in the electronic properties and Fermi surface topology of AFe2Ch2 phases are analyzed in relation to their structural parameters to explore whether these materials can be as the parent systems for new ternary iron–chalcogenide superconductors. For all these systems, similar multi-sheet Fermi surfaces consist exclusively of electronic-like sheets, two of which are 2D-like sheets in the corners of the Brillouin zone, and the third one is a closed pocket around Z. The total DOSs at the Fermi level are related with the type of anion Ch2− and their values grow in the sequence AFe2S2→AFe2Se2→AFe2Te2. Thus we assume that AFe2Se2 and AFe2Te2 phases may be considered as favorable parent systems for the search of new ternary iron–chalcogenide SCs.

Fermi-surface topology and low-lying electronic structure of the iron-based superconductor Ca10(Pt3As8)(Fe2As2)5

We report a first study of low energy electronic structure and Fermi surface topology for the recently discovered iron-based superconductor Ca10(Pt3As8)(Fe2As2)5 (the 10-3-8 phase, with Tc = 8K), via angle-resolved photoemission spectroscopy (ARPES). Despite its triclinic crystal structure, ARPES results reveal a fourfold symmetric band structure with the absence of Dirac-cone-like Fermi dots (related to magnetism) found around the Brillouin zone corners in other iron-based superconductors. Considering that the triclinic lattice and structural supercell arising from the Pt3As8 intermediary layers, these results indicate that those layers couple only weakly to the FeAs layers in this new superconductor, which has implications for the determination of its potentially novel pairing mechanism.

New concept in maximum power tracking for the control of a photovoltaic/hydrogen system

For the sustainable production of clean H2, it is essential to optimize the capture and conversion of renewable energy. In this context, this paper presents a new technique to maximize the efficiency of a photovoltaic conversion system supplying an electrolyzer. Simple, efficient and low cost maximum power point tracking algorithms to optimize energy production are proposed for the three DC/DC electronic converter topologies typically used in photovoltaic and H2 applications. The method is based on energy balance concepts and exhibits certain analogies with maximum power tracking algorithms extensively used in wind turbines that do not require measurement of the primary energy source. The algorithm provides a reference to the current controller only requiring measurement of electrical variables and solar array temperature. The current controller is implemented using sliding mode strategies. Experimental and simulation results are provided showing the effectiveness and simplicity of the proposed method.

Stability and performance analysis of a SiC-based cascode switch and an alternative solution

Wide band-gap semiconductors are most attractive as materials for power devices due to low losses, improved temperature capability and high thermal conductivity. Although silicon carbide Schottky diodes have been commercially available on the market for years, an active wide band-gap switch is still missing. Probably the best performance of upcoming devices is gained with normally-on concepts such as silicon-carbide JFETs and gallium-nitride HEMTs. However, the vast majority of power electronic topologies rely on normally-off switches. An alternative approach is the use of the cascode concept which combines a normally-on wide band-gap device with high blocking capability and a low-voltage normally-off silicon MOSFET. In this work, the performance and stability of such an arrangement is analyzed and an alternative solution is proposed.

A Review and Design of Power Electronics Converters for Fuel Cell Hybrid System Applications

This paper presents an overview of most promising power electronics topologies for a fuel cell hybrid power conversion system which can be utilized in many applications such as hybrid electrical vehicles (HEV), distributed generations (DG) and uninterruptible-power-supply (UPS) systems. Then, a multiple-input power conversion system including a decoupled dual-input converter and a three-phase neutral-point-clamped (NPC) inverter is proposed. The system can operate in both stand-alone and grid-connected modes. Simulation and experimental results are provided to show the feasibility of the proposed system and the effectiveness of the control methods.

Topological Synthesis of Tree Shaped Structures Based on a Building Blocks Hypothesis

In this paper a new approach to evolutionary controlled creation of electronic circuit connection topology is proposed. Microwave circuits consisting of a tree like connection of ideal transmission lines are considered. Assuming that a reasonable number of transmission lines in a tree network ranges from 10 to 100, the number of connection combinations is immense. From the engineering practice comes the hypothesis that any device can be decomposed into some functional building blocks consisting of one to dozen transmission lines. The variety of linking combinations in a tree with a limited depth is confined to hundreds or thousands of shapes. Therefore we can decrease the dimensionality of research space, applying evolution to building blocks only. Evolutionary algorithm (EA) which processes simultaneously the population of λ functional blocks and population of μ circuits is proposed. A μ, λ selection scheme with tournament together with specific encoding of solutions, and custom operators is implemented. The μ, λ, α EA was tested on an example of the design of a microwave transistor matching circuit.

The Optical Chained-Cubic Tree interconnection network: Topological structure and properties

Interconnection networks with optical communication links outperform others using electronic communication links when the distance is long in terms of speed and power consumption. However, for short distances, electronic network topologies are preferred due to lower material cost requirements. As a result, hybrid network topologies were constructed to combine the benefits of both types of network topologies, such as Optical Transpose Interconnection System (OTIS). This paper presents a new hybrid interconnection network topology, which is constructed using both optical and electronic links, called the Optical Chained-Cubic Tree (OCCT). This new OCCT topology is based on the Chained-Cubic Tree (CCT) interconnection network and is designed to cope with both types of binary trees; full and complete. Also, the topological properties of OCCT in terms of diameter, connectivity, degree, bisection width, and cost are presented and compared with OTIS-Mesh and CCT interconnection networks.