Transport In Junctions Research Articles

Pure spin current generation with photogalvanic effects in h-BN/graphene/h-BN van der Waals vertical heterostructures.

We have computationally demonstrated a new method for generating pure spin current with the photogalvanic effect (PGE) by constructing transport junctions using h-BN/graphene/h-BN van der Waals (vdW) heterostructure leads. It has been observed that the pure spin current without any accompanying charge current induced by the PGE can consistently be obtained, regardless of photon energy and polarization/helicity angle, as well as the specific type of polarization (linear, circular, or elliptical). The mechanism lies in the structural inversion symmetry and real space spin polarization antisymmetry of the junctions. We also found that pure spin current can be generated whether we decrease or increase the interlayer distance by applying compressive or tensile strain to the h-BN/graphene/h-BN vdW vertical heterostructure leads. Additionally, by increasing the h-BN sheets on both sides of the graphene nanoribbons for the two leads, we observed large spin splitting and were able to generate a pure spin current. These findings provide a new approach for achieving pure spin current in graphene nanoribbons and highlight the significance of vdW heterostructures in designing spintronic devices.

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Risk Assessment and Analysis of Its Influencing Factors of Debris Flows in Typical Arid Mountain Environment: A Case Study of Central Tien Shan Mountains, China

The Tien Shan Mountain range connects Central Asia with northwestern China and is a crucial transport junction between East and West Asia. It is a common location for regional debris flows, which pose a significant risk to ecological security and the safety of people and property. Nevertheless, limited knowledge exists about the distribution of disaster risks and the impacted populations. This study uses advanced machine learning techniques to identify the key natural and social factors influencing these hazards and incorporates the Social Vulnerability Index (SoVI) to assess societal vulnerability. The outcomes demonstrate that (1) the debris flow hazard in the Tien Shan Mountain area is primarily governed by the geological structure, which dictates the material source and, in turn, dictates the onset of debris flows. (2) The vulnerability demonstrates a high spatial tendency in the north and a low one in the south, with evident spatial clustering characteristics. (3) A total of 19.13% of the study area is classified as high-hazard, with specific distribution zones including the northern foothills of the Tien Shan Mountains, the low-mountain zones of the southern foothills of the Tien Shan Mountains, and the Yili Valley zone. This holistic approach offers valuable insights into the spatial distribution of risks, aiding in prioritizing disaster preparedness and mitigation efforts. Also, our findings and conclusions are beneficial for local decision makers to allocate resources effectively and promote sustainable development practices in the region.

Impact of Surrounding Infrastructure on Urban Environment: A Case Study of Karachi Metropolitan

Urban environment carries complex land-use and land cover (LULC), similarly Karachi as a metropolitan have multifaceted LULC and compact infrastructure. This study seeks to assess the impact of infrastructure of urban environment at mega city Karachi Pakistan. Approximately, fifteen different locations of metropolitan with different surroundings were evaluated based on the studied variables of surrounding such as temperature, humidity, formaldehyde (HCHO), total volatile organic compounds (TVOC) pollution, fine particulate matter (PM2.5) in air i.e., air quality, maximum noise pollution and minimum noise pollution were investigated. The readings have been collected through relevant instruments and the results have been generated through interpolation in ArcMap 10.8. The obtained results revealed that the physical factors affect the temperature and humidity conditions of the study area. While environmental and noise pollution depends on the surroundings, e.g. industrial surrounding effects on air quality, i.e. 180 recorded at industrial region of Korangi, while construction sites are catalysts of noise pollution and highest noise pollution are recorded at North-Nazimabad. Cancer causing substance, i.e. formaldehyde found along the petrol pumps, airports and transportation junctions ranges up to 0.99 ppm near Jinnah International airport and mass transit location of Shahrah e Faisal. While total volatile compound pollution has been found along the Malir catchment area, i.e. 0.4 mg/m3. The lifestyle of Karachiites need to be transform there is a dire need to think about physical and mental concord of the citizens of metropolitan. Similarly, government should play some positive actions and introduced green and environmental friendly technology to control air and noise pollution.

Quantum Interference Effects on Charge Transport in Molecular Electronic Junctions

Quantum Interference Effects on Charge Transport in Molecular Electronic Junctions

Phase dependence of thermal transport in graphene Josephson junctions

Phase dependence of thermal transport in graphene Josephson junctions

Seismic vulnerability analysis on an extra-large highway-railway dual-used arch bridge

The seismic vulnerability analysis is of great important for the design, operation and maintain. The selected extra-large highway and railway dual-used arch bridge contains high geometric nonlinearity and is one of the transportation junctions. Therefore, it is necessary to conduct seismic response analysis. The research results can provide reference for the seismic design and seismic response analysis of target bridge and similar typed bridges. Thus, it has high theoretical value for the design and promotion of similar bridges. This paper starts with a theoretical analysis, using the finite element software LS-DYNA to build a dynamic calculation model of the real bridge and carry out modal and time response analyses. The strength, vulnerable components and stability of the bridge under three-way seismic action at for different earthquake excitation waves (Wenchuan earthquake, Chichi earthquake, Kobe earthquake and El-Centro earthquake) are investigated. Through analysis and comparison of numerical calculations, the seismic performance of the target bridge was comprehensively evaluated.

Flow rectification in a micro-nanochannel junction: Interplay of channel geometry and interfacial properties for directional transport

The linear correspondence between flow rate and pressure drop for low Reynolds number hydrodynamics is often a constraint for the realization of miniaturized fluid circuits with selective junctions. Here we devise a micro-nanochannel junction with the directional flow in the nanochannel achieved by a combination of junction geometry and wall functionalization. The system can be compared to a fluid diode with parity-breaking between pressure drop and flow rate in the nanochannel junction with increasing flow rates in a particular configuration and negligible throughput in the reverse direction. This directional junction transport is tuned with slip length, characterizing channel wall functionalization as the bias parameter. Tuning the transport or leakage at a junction is key to engineering various applications. Such junctions are ubiquitous in systems like capillary blood flow, desalination systems, energy storage devices, etc. The resulting flow physics, thus unraveled, is an amalgamation of various factors which leads to a flow rectification system. We have delineated the effect of the confinement of the channel, the slip, and the geometry of the nanochannel towards the selective nature of the resulting configuration. We have successfully characterized a system to generate flow anisotropy while transporting fluid in different directions using numerical techniques. Additionally, our work demonstrates, for the first time, that a common definition of slip coefficient may be associated with three different flow regimes, which correspond to the order of magnitude of slip length relative to the channel dimensions thus providing a unifying key to engineer substrates and geometries towards designing fluid circuits.

Experience in the design and construction of service facilities located at ‏transport hubs

The article analyzes the latest research, experience in the design and construction of transport interchanges. The main trends and directions of the architectural and planning solution of the service facilities located in them have been identified. The formation of service facilities is influenced by the dynamics of the development of nearby districts and residential areas, the urban development situation, and social and economic conditions. Direct interdependence is observed - provided the population increases in the adjacent residential areas and the production potential of local industrial enterprises increases several times, while the traffic load of the relevant transport arteries, transfer stations and transport junctions and nodes increases. Transport interchanges and stations of the city of Kyiv, Ukraine were analyzed. One of the largest transport intersections was found to be located in the East: in China (Beijing, Shanghai), South Korea (Seoul), Japan (Tokyo, Kyoto). The classification is given depending on the functional load, location in the city system, annual volume of passengers, type of service by size (small, medium, large); type of volumetric-spatial solution. The main principles of the formation of volumetric and spatial solutions are formulated. In the development of the planning structure, the following main functional blocks were identified: transport and transport arteries; storage areas and platforms; communications and transitions (vertical and horizontal, transitions, stairs, elevators, escalators); service of regular and rest transit passengers; trade and entertainment; "intercepting" parking lots and city public transport stops. There are three main types of planning configuration of junctions and landfills, determined in particular by the shape of the plots under construction and the urban planning situation.

The Spread of Snow Avalanches at Transport Junctions in the Mountainous Regions of Georgia

The Spread of Snow Avalanches at Transport Junctions in the Mountainous Regions of Georgia

Full quantum theory for magnon transport in two-sublattice magnetic insulators and magnon junctions

Full quantum theory for magnon transport in two-sublattice magnetic insulators and magnon junctions

Flexible and Printable Composite Ink for Thermal Management of Soft Electronics

AbstractSince heat generation in electronic devices causes thermal failure, heat dissipation is of critical importance. Furthermore, deformable devices are subjected to mechanical stress, therefore, mechanically stable thermal management material should be considered. Herein, a strategy for printable, thermally conductive, and mechanically stable composite ink for thermal management is introduced. Based on the galvanic replacement between eutectic gallium indium (EGaIn) nanoparticles and silver (Ag) flakes, decoration of the EGaIn nanoparticles on Ag flakes is resulted from the difference in standard reduction potential between Ag, Ga, and In. The resultant alloy formation(Ag–Ga or Ag–In) serves as the thermal transport junction between Ag flakes, leading to high thermal and electrical conductivity (≈140 W mK−1 and ≈106 S m−1, respectively). In addition, owing to the polymer binder, the printed ink is mechanically stable on a substrate exhibiting stable thermal conductivity and sheet resistance under the cyclic bending test. Notably, the heat dissipation of the light‐emitting diode (LED) showed better performance when applied with the developed composite ink compared to commercial Ag paste and thermal paste. The junction temperature of the LED is reduced effectively, resulting in a longer lifetime of the LED. The thermal management solution can be utilized in next‐generation soft electronics.

Time-Dependent Density Matrix Renormalization Group Method for Quantum Transport with Phonon Coupling in Molecular Junction.

Quantum transport in molecular junctions has attracted great attention. The charge motion in a molecular junction can cause geometric deformation, leading to strong electron phonon coupling, which was often overlooked. We have formulated a nearly exact method to assess the time-dependent current and occupation number in the molecular junction modeled by the electron-phonon coupled bridge state using the time-dependent density matrix renormalization group (TD-DMRG) method. The oscillation period and amplitude of the current are found to be dependent on the electron phonon coupling strength and energy level alignment with the electrodes. In an attempt to better understand these phenomena, we have devised a new approximation that explains the bistability phenomenon and the behavior of steady currents in the strong electron-phonon coupling regime. Comparisons have been made with the multilayer-multiconfiguration time-dependent Hartree (ML-MCTDH) method and the analytical result in the purely electronic limit. Furthermore, we explore the entropy of different orderings, extending to the electron phonon model problems. Regarding finite temperature, the thermal Bogoliubov transformation of both fermions and bosons is used and compared with imaginary time evolution results.

Manipulating Quantum Interference between σ and π Orbitals in Single-Molecule Junctions via Chemical Substitution and Environmental Control.

Understanding and manipulating quantum interference (QI) effects in single molecule junction conductance can enable the design of molecular-scale devices. Here we demonstrate QI between σ and π molecular orbitals in an ∼4 Å molecule, pyrazine, bridging source and drain electrodes. Using single molecule conductance measurements, first-principles analysis, and electronic transport calculations, we show that this phenomenon leads to distinct patterns of electron transport in nanoscale junctions, such as destructive interference through the para position of a six-membered ring. These QI effects can be tuned to allow conductance switching using environmental pH control. Our work lays out a conceptual framework for engineering QI features in short molecular systems through synthetic and external manipulation that tunes the energies and symmetries of the σ and π channels.

Competition of Quasiparticles and Magnetization Noise in Hybrid Ferromagnetic Transmon Qubits

The coexistence between ferromagnetic ordering and superconducting transport in tunnel ferromagnetic Josephson junctions (SFS JJs) accounts for a wide range of unconventional physical properties. The integration of both insulating ferromagnets or multi-layered insulator-ferromagnet barriers allows to combine ferromagnetic switching properties with peculiar low quasiparticle dissipation, which could enhance the capabilities of SFS JJs as active elements in quantum circuits. Here we show that split-transmon qubits based on tunnel ferromagnetic JJs realize an ideal playground to study noise fluctuations in ferromagnetic Josephson devices. By considering the transport properties of measured Al-based tunnel SFS JJs, we report on a theoretical study of the competition between intrinsic magnetization fluctuations in the barrier and quasiparticles dissipation, thus providing specific operation regimes to identify and disentangle the two noise sources, depending on the peculiar properties of the F layer and F/S interface.

First-Principles Studies on Spin-Dependent Transport of Magnetic Junctions with Half-Metallic Heusler Compounds

Two types of magnetoresistance (MR), i.e., tunnel magnetoresistance (TMR) and current perpendicular to plane giant magnetoresistance (CPP-GMR), are theoretically discussed for systems with half-metallic (HFM) Co-based full Heusler compounds. In TMR, the non-collinear spin structure at the Co2MnSi(CMS)/MgO(001) interface that results from thermal spin fluctuations significantly reduced the TMR ratio at room temperature (RT). Enhancement of the exchange stiffness of CMS/MgO was essential to suppress the reduction in TMR at RT. Furthermore, it is proposed that inserting of a B2-CoFe layer between CMS and MgO is a promising way to enhance the interface exchange stiffness constant. In CPP-GMR, the interface spin asymmetry γ in the Valet-Fert model was essential to enhance GMR at RT, because the temperature dependence of γ in experiments was much larger than that of the bulk spin asymmetry β. I showed that the experimental CPP-GMR ratio increases with the decrease in the theoretical resistance-area product RPA, which is roughly consistent with the RP dependence of γ. This means that matching of the conductive channel between HMF and a non-magnetic metallic spacer is a key parameter to enhance γ. These findings will be very important for room temperature spintronics devices applied in future artificial intelligence hardware.

The spin-polarized tunnel current and the spin-transfer torque in triple-barrier junctions with external electrodes and quantum wells made of ferromagnetic materials

The electron transport in triple-barrier junctions consisting of external ferromagnetic layers and three non-magnetic barriers separated by two inner ferromagnetic layers is analysed. It is assumed that the magnetic moments in the external electrodes are oriented in the same direction, whereas the magnetic moments of the inner layers can form any angle with this direction. The possibility of the gigantic enhancement of the normal torque component has been found in the junctions with a non-colinear orientation of magnetic moments in the inner layers. This enhancement may be much larger than in the double junctions. The current and the in-plane torque are most amplified when the quantum-well states in both inner layers have similar energies and can form the complex resonant states located slightly below the Fermi level. When the tunnelling by these complex resonant states occurs, the torque is greatest in the magnetic configuration other than that where the current is maximally enhanced. Additionally, the angular dependence of the torque differs significantly from that observed in single tunnel junctions.

Secondary Structure-Dependent Charge Transport in iLOV Protein Junctions.

The composition and structure of proteins are crucial for charge migration in the solid-state charge transport (CTp). Despite much progress, it is still challenging to explore the relationship between conformational change and CTp in the complex protein system. Herein, we design three improved light-oxygen-voltage (iLOV) domains, and efficiently regulate the CTp of the iLOV self-assembled monolayers (SAMs) by pH induced conformation variation. The current density can be controlled in the range of one order of magnitude. Interestingly, the CTp of iLOV displays negative linear relations with the β-sheet contents. Single-level Landauer fitting and transition voltage spectroscopy analysis suggest that β-sheet-dependent CTp would be related to the coupling between iLOV and electrodes. This work proposes a new strategy to explore the CTp in complex molecular system. Our findings deepen the understanding on protein structure-CTp relationship, and provide predictive mode of protein CTp responses for the design of functional bioelectronics.

Tuning Charge Transport of Oligopeptide Junctions via Interfacial Amino Acids†

Comprehensive SummaryThe charge transport through peptides can imitate the corresponding processes in more complicated proteins, enabling us to develop high‐performance bioelectronic devices and to understand the mechanisms of biomolecular recognition and information transfer. While charge transport modulation through individual peptides has been achieved via various covalent strategies, the intermolecular modulation is still very challenging, which may capture the charge transport between proteins. To tackle this challenge, we used well‐defined self‐assembled monolayers (SAMs) of oligopeptides as a model to imitate the interface of proteins and explored an interfacial amino acid strategy for charge transport modulation. We showed that non‐covalently interfaced charged amino acids (e.g., arginine) effectively attenuated the charge transport of glutamic acid terminated polyglycine peptide SAMs. By analyzing the relationship of the charge transport with the molecular frontier orbital relative to the Fermi energy level of the electrode, the molecule‐electrodes coupling (Γ), and the trends in skewness and kurtosis with voltage and the dielectric constant (εr), we showed that the attenuation was from the decreased Γ and the reduced polarizability. We present an efficient strategy to modulate the charge transport of oligopeptide‐SAM junctions by intermolecular interactions, which will advance our understanding of charge transport in biological systems and facilitate developing future electronics.

Electrically controllable spin polarization in collinear antiferromagnetic junctions

Antiferromagnetic spintronics is a rapidly growing subfield of spintronics in condensed-matter physics and information technology. Electrical current in collinear antiferromagnetic materials is typically spin unpolarized, limiting the realization of antiferromagnetic spintronics effects. Here we study the transport in the collinear antiferromagnetic junctions by applying a transverse electric field E y to the antiferromagnets (AFs). The band structures of the collinear AFs may become spin-polarized when the combined time reversal and lattice translation symmetry is broken by E y . The separation between spin-up and spin-down bands is controlled by E y . Full spin polarization originating from spin-polarized states near the band gap’s edges is observed at high exchange energy. In particular, as E y increases, the region capable of generating high spin polarization broadens due to the increased separation between spin-up and spin-down bands. The amplitude and sign of spin polarization can be controlled by E y . These characteristics indicate that collinear AF materials are ideal for future spintronics applications.