Electronic Topology Research Articles

Substrate-limited helical edge states

We derived analytical results for the gapless edge states of two-dimensional topological insulators in the presence of electron--surface optical (SO) phonon interaction due to substrates. We followed an analytical algorithm, called the Lee-Low-Pines variational approximation in the conventional polaron theory, to examine the substrate-induced effects on both bulk and edge states of a two-dimensional topological insulator within the frame work of the Bernevig-Hughes-Zhang (BHZ) model. By implementing this algorithm, we propose a phonon-dressed BHZ Hamiltonian which allows one to investigate the effects of various substrates not only on bulk states but also on the associated gapless helical edge states (HESs). We found that both the bulk and HESs are significantly renormalized in the momentum space due to the substrate-related polaronic effects. The model we developed here clarifies which substrates favor the HESs of the quantum spin Hall system and which do not. Correspondingly, our work demonstrates that the substrate-related polaronic effects have a significant role in the emergence of HESs. In other words, we show that SO phonons due to substrates modify the electronic band topology of topological insulators together with the associated HESs, and therefore, they can be used to tune quantum phase transitions between topological insulators and nontopological ones.

Pressure-induced topological phase transition in noncentrosymmetric elemental tellurium

Recent progress in understanding the electronic band topology and emergent topological properties encourage us to reconsider the band structure of well-known materials including elemental substances. Controlling such a band topology by external field is of particular interest from both fundamental and technological viewpoints. Here we report possible signatures of the pressure-induced topological phase transition from a semiconductor to a Weyl semimetal in elemental tellurium probed by transport measurements. Pressure variation of the periods of Shubnikov-de Haas oscillations, as well as oscillation phases, shows an anomaly around the pressure theoretically predicted for topological phase transition. This behavior is consistent with the pressure-induced band deformation and resultant band-crossing effect. Moreover, effective cyclotron mass is reduced toward the critical pressure, potentially reflecting the emergence of massless linear dispersion. The present result paves the way for studying the electronic band topology in well-known compounds and topological phase transition by the external field.

Controlling a Van Hove singularity and Fermi surface topology at a complex oxide heterostructure interface

The emergence of saddle-point Van Hove singularities (VHSs) in the density of states, accompanied by a change in Fermi surface topology, Lifshitz transition, constitutes an ideal ground for the emergence of different electronic phenomena, such as superconductivity, pseudo-gap, magnetism, and density waves. However, in most materials the Fermi level, {E}_{{rm{F}}}, is too far from the VHS where the change of electronic topology takes place, making it difficult to reach with standard chemical doping or gating techniques. Here, we demonstrate that this scenario can be realized at the interface between a Mott insulator and a band insulator as a result of quantum confinement and correlation enhancement, and easily tuned by fine control of layer thickness and orbital occupancy. These results provide a tunable pathway for Fermi surface topology and VHS engineering of electronic phases.

A Access of SST Converter Topologies: Control & Modulation Techniques

The Solid State Transformer (SST) is the emerging power electronics based key component of distribution system. In this paper a comparison of SST converter topologies with control and modulation techniques is presented. The main focus is on the use of SST for various applications based on the features offered by different converter topologies with different control techniques. The review is carried out by comparing these power electronics topologies based on their structure, advantages, limitations and their control techniques suitable for different applications such as green energy source integration to grid, traction, controlling of electrical machines, use as a Distributed Generators, due to powerful and attractive features of SST. The three stage SST is considered and compared for converter topologies with their control and modulation schemes which will help to identify the suitability of SST for the application

Theoretical investigation on the interaction mechanism of FOX-7/AP mixed crystals

ABSTRACTHerein, in order to determine the formation feasibility of 1,1-diamino-2,2-dinitroethylene (FOX-7)/ ammonium perchlorate (AP) mixed crystals, three configurations of FOX-7/AP composites (FOX-7/AP1, FOX-7/AP2, FOX-7/AP3) were optimised, and the structures of FOX-7/AP mixed crystals were constructed. Then the electrostatic potential, binding energy and electronic density topology of FOX-7/AP composites were calculated by using the density functional theory. Finally, the radial distribution function between H atoms and O atoms of FOX-7/AP mixtures was calculated through molecular dynamics. As demonstrated by the results, there are hydrogen bond interactions in three configurations of FOX-7/AP composites. The interaction energies of FOX-7/AP1, FOX-7/AP2 and FOX-7/AP3 are 8.396, 20.537 and 38.189 kJ▪mol−1, respectively. The order of the electron density ρ(r) at the bond critical point (BCP) of three FOX-7/AP composites is FOX7-AP3 > FOX7-AP2 > FOX7-AP1. There are apparent peaks at the range of 0.11–0.31 nm and 0.31–0.5 nm for FOX-7(10-1)/AP, FOX-7(011)/AP, FOX-7(101)/AP mixed crystals. The interaction strength of the hydrogen bond is greater than that of strong van der Waals force. Therefore, it is feasible to combine FOX-7 with AP to form mixed crystals. As the content of AP in the mixed crystal is on the rise, the oxygen balance of the system shows a gradually increasing trend.

Electronic Structure of a Graphene-like Artificial Crystal of NdNiO3.

Artificial complex-oxide heterostructures containing ultrathin buried layers grown along the pseudocubic [111] direction have been predicted to host a plethora of exotic quantum states arising from the graphene-like lattice geometry and the interplay between strong electronic correlations and band topology. To date, however, electronic-structural investigations of such atomic layers remain an immense challenge due to the shortcomings of conventional surface-sensitive probes with typical information depths of a few angstroms. Here, we use a combination of bulk-sensitive soft X-ray angle-resolved photoelectron spectroscopy (SX-ARPES), hard X-ray photoelectron spectroscopy (HAXPES), and state-of-the-art first-principles calculations to demonstrate a direct and robust method for extracting momentum-resolved and angle-integrated valence-band electronic structure of an ultrathin buckled graphene-like layer of NdNiO3 confined between two 4-unit cell-thick layers of insulating LaAlO3. The momentum-resolved dispersion of the buried Ni d states near the Fermi level obtained via SX-ARPES is in excellent agreement with the first-principles calculations and establishes the realization of an antiferro-orbital order in this artificial lattice. The HAXPES measurements reveal the presence of a valence-band bandgap of 265 meV. Our findings open a promising avenue for designing and investigating quantum states of matter with exotic order and topology in a few buried layers.

Technological Advancement in PMSG Based Wind Energy Conversion Systems: Issues and Challenges

Background: Since its beginning in 1980, wind energy generation has gained newer heights and emerged as the most promising renewable energy technology at present. Wind turbine rating has increased from few kW to MW and now multi-MW turbines are also available and in operation too. Introduction: Impact of wind turbines on the grid has significantly increased with increased penetration of wind power into the grid. In order to improve the performance characteristics of the wind turbines, and make them suitable for grid integration, more advanced generators, control schemes, and power converters are required. Latest wind energy market trends and research articles reflect the popularity and market capture of Permanent Magnet Synchronous Generator (PMSG) for wind turbine applications. Method: The present work is dedicated to important electrical aspects concerning PMSG based wind energy conversion system. Starting with the technological development of wind turbine, state-of-the-art PMS based wind turbine concepts with power electronic converter topologies are discussed. Result: A comprehensive analysis of converter topology, grid integration, integration issues, and future research and technology trends are presented.In addition steady state performance analysis of PMSG based wind turbine is presented depicting issues with different control schemes. Conclusion: The study presented in this paper envisages help to the researcher in this area by providing them clear insight of various power electronic interfaces, their control complexities and various issues of concern. In addition we are assure that steady state analysis presented in this paper will attract the newcomers in this field of research.

Improved powered bus communication technique based on PD‐TDMT for distributed power system (DPS)

For many distributed power systems (DPSs) such as light-emitting diode lighting and battery management, communication is essential. This study presents an improved method of integrating power transfer and communication through a common bus by applying the concept of power/data time division multiplexing transmission (PD-TDMT). The proposed method employs power electronic topologies as the basic circuits to create the power transfer system and utilises the power transmission intervals for communication. Compared with conventional communication techniques in DPS, the proposed method has the advantages of simple implementation, enhanced noise immunity and higher output power capacity. The general structure of PD-TDMT systems is presented, which includes power sourcing equipment (PSE) and powered devices (PDs). A series of PSE and PD circuits are derived based on dc–dc topologies. The timing sequence of power transfer and communication is given. To suppress the common-mode interferences under the high-power condition, a balanced power transmission system is also proposed. Besides, the termination circuits are discussed in detail under the long-distance transmission condition. Finally, the proposed method and theoretical analysis are verified by experiment.

Eigenvalue crossings in Floquet topological systems

The topology of electrons on a lattice subject to a periodic driving is captured by the three-dimensional winding number of the propagator that describes time-evolution within a cycle. This index captures the homotopy class of such a unitary map. In this paper, we provide an interpretation of this winding number in terms of local data associated to the the eigenvalue crossings of such a map over a three dimensional manifold, based on an idea from Nathan and Rudner, New Journal of Physics, 17(12) 125014, 2015. We show that, up to homotopy, the crossings are a finite set of points and non degenerate. Each crossing carries a local Chern number, and the sum of these local indices coincides with the winding number. We then extend this result to fully degenerate crossings and extended submanifolds to connect with models from the physics literature. We finally classify up to homotopy the Floquet unitary maps, defined on manifolds with boundary, using the previous local indices. The results rely on a filtration of the special unitary group as well as the local data of the basic gerbe over it.

A Review on Communication Standards and Charging Topologies of V2G and V2H Operation Strategies

Electric vehicles are the latest form of technology developed to create an environmentally friendly transportation sector and act as an additional energy source to minimize the demand on the grid. This comprehensive research review presents the vehicle-to-grid (V2G) and the vehicle-to-home (V2H) technologies, along with their structures, components, power electronic topologies, communication standards, socket structure, and charging methods. In addition, the charging topologies in V2G and V2H are given in detail. This study is planned as a useful guide for future studies that can be achieved in that it compares the results obtained and analyzes the studies in the literature, finding the advantages and disadvantages of charging topologies in V2G and V2H.

Discovery of topological Weyl fermion lines and drumhead surface states in a room temperature magnet.

Topological matter is known to exhibit unconventional surface states and anomalous transport owing to unusual bulk electronic topology. In this study, we use photoemission spectroscopy and quantum transport to elucidate the topology of the room temperature magnet Co2MnGa. We observe sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase. On the surface of the magnet, we observe electronic wave functions that take the form of drumheads, enabling us to directly visualize the crucial components of the bulk-boundary topological correspondence. By considering the Berry curvature field associated with the observed topological Weyl fermion lines, we quantitatively account for the giant anomalous Hall response observed in this magnet. Our experimental results suggest a rich interplay of strongly interacting electrons and topology in quantum matter.

Review of AC-DC power electronic converter topologies for power factor correction

<p>Increased harmonic content and low power factor in power systems caused by power converters have been of great concern. To overcome this, several converter topologies employing advanced semiconductor devices and control schemes have been proposed. The aim of this paper is to identify a low cost, small size, efficient and reliable ac to dc converter to meet the input performance index of uninterrupted power supply. In this paper, comparison between three converters namely AC-DC Cuk rectifier, Fly back converter & Interleaved SEPIC converter have been carried out. For the above converters both bridged and bridgeless topologies have been analysed. The working of all the three types of converter has been illustrated with relevant waveforms followed by the simulation results. Comparison of the three converters have been done based on the parameters namely Displacement Factor, Supply Power Factor& supply THD. The results are verified.</p>

Topology in time-reversal symmetric crystals

Topology and symmetry are cornerstones of modern condensed matter physics. They are not independent, and the symmetries of a particular material determine how many topologically distinct phases it may host. Unlike external symmetries, such as time-reversal symmetry, the relation between atomic lattice symmetries and electron topology is not known in general. The authors present an algorithm for classifying all time-reversal symmetric crystalline topological insulators. It yields an intuitive picture of the relations between topological invariants, and predicts new invariants in particular lattices.

Investigation of 3D pharmacophore of N-benzyl benzamide molecules of melanogenesis inhibitors using a new descriptor Klopman index: uncertainties in model.

We used a new descriptor called the Klopman index in our software of the "molecular comparative electron topology" (MCET) method to reduce the uncertainty resulting from the descriptors used in QSAR studies. The 3D pharmacophore model (3D-PhaM), which can demonstrate three-dimensional interaction between the ligand -receptor (L-R), is only possible with local reactive descriptors (LRD). The Klopman index, containing both Coulombic and frontier orbital and interactions of atoms of the ligand, is a good LRD. Molecular conformers having the best matching atoms with the template conformer can be selected as one of the most suitable spatial structures for interaction with the receptor, and the LRD values of the atoms in this conformer serve to determine 3D-PhaM. The 3D-PhaM of the N-benzyl benzamide derivatives, such as the melanogenesis inhibitor, was determined by ligand-based MCET and confirmed by the structure-based FlexX docking method. For compounds of the training set (42) and the external cross validation test set (6), the Q2 (0.862) and R2 (0.913) of the statistical parameters were calculated, respectively, and were checked by rm2 (0.85) of the stringent validation.

Influence of an Anomalous Temperature Dependence of the Phase Coherence Length on the Conductivity of Magnetic Topological Insulators.

Magnetotransport constitutes a useful probe to understand the interplay between electronic band topology and magnetism in spintronic devices. A recent theory of Lu and Shen [Phys. Rev. Lett. 112, 146601 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.146601] on magnetically doped topological insulators predicts that quantum corrections Δκ to the temperature dependence of conductivity can change sign across the Curie transition. This phenomenon has been attributed to a suppression of the Berry phase of the topological surface states at the Fermi level, caused by a magnetic energy gap. Here, we demonstrate experimentally that Δκ can reverse its sign even when the Berry phase at the Fermi level remains unchanged. The contradictory behavior to theory predictions is resolved by extending the model by Lu and Shen to a nonmonotonic temperature scaling of the inelastic scattering length showing a turning point at the Curie transition.

Power‐take‐off topology comparison for a wave energy converter

Wave Energy Converters (WECs) generally use a Mechanical Power-Take-Off (MPTO) involving hydraulics or gearing to optimise the extraction of energy from the incoming waves before converting it into electrical energy via a high speed rotating generator. This simplifies the design of the Electrical Power Conversion System (EPCS). Further, it facilitates the use of mechanical energy storage such as hydraulic accumulators to reduce the peaky nature of the power flow and allows the WEC resonant frequency to be tuned for maximum energy capture. This work compares two power electronic converter topologies for an Electrical PTO (EPTO). This EPTO is intended to replace the aforementioned MPTO and generator with a Permanent Magnet Linear Machine (PMLM) directly coupled to the WEC. The compared topologies comprise either a Current Source Converter (CSC) or a Voltage Source Converter (VSC) as the generator interface working in combination with a DC-DC converter and an Energy Storage System (ESS). The principle differences between the two topologies are explored and losses are evaluated in a modular EPCS working with a WEC. Wide-bandgap power electronic switches are assumed for both topologies over a range of switching frequencies. The evaluation concludes that the CSC topology is advantageous at higher switching frequencies.

Reply to Correspondence on “Core Electron Topologies in Chemical Compounds: Case Study of Carbon versus Silicon”

AbstractIn their Correspondence, von Szentpály, Schwarz, Stoll, and Werner claim that the main conclusions of our Communication previously published in this journal are based on computational artifacts and oversimplified models. We clarify the justification of our simple one‐electron model to describe one‐electron physics, and refute their criticism based on what they call “computational artifacts.” We remind that our main conclusion on the crucial role of qualitative changes in core electron wavefunctions is evidenced not only by wavefunction topologies the complainants cling to, but also by several other physical observables, which remain unrefuted. Hence, the conclusions of our original Communication stand.

Composition and stacking dependent topology in bilayers from the graphene family

We present a compositional and structural investigation of silicene, germanene, and stanene bilayers from first principles. Due to the staggering of the individual layers, several stacking patterns are possible, most of which are not available to the bilayer graphene. This structural variety, in conjunction with the presence of the spin-orbit coupling, unveils a diversity of the electronic properties, with the appearance of distinct band features, including orbital hybridization and band inversion. We show that for particular cases, the intrinsic spin Hall response exhibits signatures of nontrivial electronic band topology, making these structures promising candidates to probe Dirac-like physics.

Research and Application of Low Voltage Ride Through Testing Device for Low Voltage Frequency Converter in Thermal Power Plant

In order to improve the Low Voltage Ride through (LVRT) level of the low voltage auxiliary frequency converter in the thermal power plant and effectively solve problems including the inaccurate drop time of voltage drop device, which is controlled by the switching structure of the traditional multi-winding transformer, excessive magnetizing inrush current occurs during the closing process, and the 30KW testing device for LVRT of the frequency converter in the thermal power plant is developed. It is designed with a three-phase four-wire back-to-back power electronic topology, together with adaptive fuzzy PI control algorithm. They can precisely set the voltage drop amplitude and time, ensuring automatic periodic cycle test controlled by upper computer. A LVRT field experiment has been carried out on low-voltage auxiliary frequency converter both before and after the transformation in a thermal power plant in Jiangxi Province. It proves that the dynamic response time of the power electronic voltage drop device is less than 5ms, the harmonic content in the converter voltage output is less than 0.5%. Additionally, the device boasts convenient operation and well-developed protection mechanism.

72‐1: Invited Paper: Critical Components in Solid‐State Lighting

Solid state lighting (SSL) has become the most preferred and efficient general lighting. This paper presents a comprehensive overview of critical components needed for SSL with the primary focus being on the critical components including those related to passive and active electronic components, circuit topologies, tradeoffs, agency and regulatory requirements.