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Using computer simulations, we have studied the percolation and the electrical conductance of two-dimensional, random percolating networks of curved, zero-width metallic nanowires. We mimicked the curved nanowires using circular arcs. The percolation threshold decreased as the aspect ratio of the arcs increased. Comparison with published data on the percolation threshold of symmetric quadratic Bézier curves suggests that when the percolation of slightly curved wires is simulated, the particular choice of curve to mimic the shape of real-world wires is of little importance. Considering the electrical properties, we took into account both the nanowire resistance per unit length and the junction (nanowire/nanowire contact) resistance. Using mean-field approximation (MFA), we derived the total electrical conductance of nanowire-based networks as a function of their geometrical and physical parameters. The MFA predictions have been confirmed by our Monte Carlo numerical simulations. For our random homogeneous and isotropic systems of conductive curved wires, the electric conductance decreased as the wire shape changed from a stick to a ring when the wire length remained fixed. [ABSTRACT FROM AUTHOR]

Using Monte Carlo simulation, we studied the electrical conductance of two-dimensional films. The films consisted of a poorly conductive host matrix and highly conductive rodlike fillers (rods). The rods were of various lengths, obeying a log-normal distribution. They were allowed to be aligned along a given direction. The impacts of the length dispersity and the extent of the rod alignment on the insulator-to-conductor phase transition were studied. Two alternative computational approaches were compared. Within Model I, the films were transformed into resistor networks with regular structures and randomly distributed conductances. Within Model II, the films were transformed into resistor networks with irregular structures but with equal conductivities of the conductors. A comparison of the models evidenced similar behavior in both models when the concentration of fillers exceeded the percolation threshold. However, a fairly fine mesh should be used in Model I to obtain a reasonable estimation of the electrical conductance. The electrical conductance is slightly overestimated in Model I. In anisotropic systems, the length dispersity of fillers has a more pronounced effect on the electrical conductance along the direction of the rod alignment. Some analytical results were obtained: (i) the relationship between the number of fillers per unit area and the transmittance of the films within Model I and (ii) the electrical conductance of the films for dense networks within Model II. [ABSTRACT FROM AUTHOR]

Conducting behavior of two-dimensional (2D) disordered nanowire networks (DNNs) is studied. We find that the length-ratio (ηcp) of conducting paths to all nanowires in the network plays a key role in determining the network conductivity. An algorithm is designated to monitor the formation of conducting paths in the networks and the evolution of network conductance at the same time. As either the area fraction or length of nanowires increases, the length-ratio (ηcp) of the conducting paths expands; meanwhile, the network conductance increases. The network conductance is normalized by the conductance of the regular network so that normalized network conductivity (σ) is obtained. A linear relationship is observed when plotting r against ηcp. An equation of σ = 2(ηcp -0:5) is obtained when ηcp is higher than the threshold. It could fit most part of the simulated plots, except for the region near ηcp ~ 0:5. 2D transparent and conductive films are built from randomly arranged silver nanowires. Linear behavior is also observed, with the slope less than 2, which is due to the existence of the junction resistance between nanowires. The obtained equation is in agreement with the previous result of the Effective Medium Theory. Finally, the length-ratio (ηcp) could serve as a basic topological parameter in describing the conducting behavior of DNNs. [ABSTRACT FROM AUTHOR]

Conducting behavior of two-dimensional (2D) disordered nanowire networks (DNNs) is studied. We find that the length-ratio ( η c p ) of conducting paths to all nanowires in the network plays a key role in determining the network conductivity. An algorithm is designated to monitor the formation of conducting paths in the networks and the evolution of network conductance at the same time. As either the area fraction or length of nanowires increases, the length-ratio ( η c p ) of the conducting paths expands; meanwhile, the network conductance increases. The network conductance is normalized by the conductance of the regular network so that normalized network conductivity (σ) is obtained. A linear relationship is observed when plotting σ against η c p . An equation of σ = 2 (η c p − 0.5) is obtained when η c p is higher than the threshold. It could fit most part of the simulated plots, except for the region near η c p ∼ 0.5. 2D transparent and conductive films are built from randomly arranged silver nanowires. Linear behavior is also observed, with the slope less than 2, which is due to the existence of the junction resistance between nanowires. The obtained equation is in agreement with the previous result of the Effective Medium Theory. Finally, the length-ratio ( η c p ) could serve as a basic topological parameter in describing the conducting behavior of DNNs. [ABSTRACT FROM AUTHOR]

This paper presents theoretical investigations on the interfacial thermal conductance (Kapitza conductance) in both monotype Si/Ge (cubic 3C) and polytype (cubic 3C/hexagonal 2H) Ge interfaces by using full band extensions of diffusive and acoustic mismatch models. In that aims, phonon dispersions in the full 3D Brillouin zone have been computed via an atomistic adiabatic bond charge model. The effects of crystal orientation are investigated, and the main phonon modes involved in heat transfer are highlighted. According to our calculations, polytype interfaces without any mass mismatch but with a crystallographic phase mismatch exhibit a thermal conductance very close to that of Si/Ge interfaces with a mass mismatch but without any phase mismatch. Besides, the orientations of Ge polytype interface that have been observed experimentally in nanowires, i.e., along [115]/[5051], exhibit the lowest interfacial conductance and thus may offer new opportunities for nanoscale thermoelectric applications. [ABSTRACT FROM AUTHOR]

We used a range of scanning tunnelling microscopy (STM)-based methods to conduct a detailed study of single molecule junction conductance enhancement upon charge transfer complex formation, using bis(thiaalkyl)arene molecular wires as electron donors and tetracyanoethylene (TCNE) as an electron acceptor. Using the "hard" STM break junction (STM-BJ) method, in which a Au STM tip is pushed into a Au substrate and then withdrawn in the presence of molecules, we see a single, very broad, peak in the resulting conductance histogram when all data are used; the conductance enhancement is 25-fold for a terthiophene donor and 15-fold for a phenyl group. After rational data selection, in which only current-distance curves that contain a current plateau >0.2 nm long are used in the conductance histogram, three sharper peaks are resolved in the histograms for the charge transfer complexes; two substantially lower-conductance peaks are resolved for the uncomplexed molecules. Using the "soft" STM I(s) technique, in which initial contact between tip and substrate is avoided and the current limit is about an order of magnitude lower, we were able to resolve two peaks for the uncomplexed molecules depending upon the initial set point current (i.e., tip height), one at the same value as the lower of the two data-selected STM-BJ histogram peaks and an additional peak beyond the low-current limit for the STM-BJ experiment. For the terthiophene, the low, medium, and high conductance peaks for the TCNE complex are, respectively, ca. 70, 70, and 46 times higher in conductance than the corresponding peaks for the free molecule. [ABSTRACT FROM AUTHOR]

We have simultaneously measured conductance and thermoelectric power (TEP) of individual silicon and germanium/silicon core/shell nanowires in the field effect transistor device configuration. As the applied gate voltage changes, the TEP shows distinctly different behaviors while the electrical conductance exhibits the turn-off, subthreshold, and saturation regimes, respectively. At room temperature, peak TEP value of ∼300 μV/K is observed in the subthreshold regime of the Si devices. The temperature dependence of the saturated TEP values is used to estimate the carrier doping of Si nanowires. [ABSTRACT FROM AUTHOR]

We investigated the behavior of the zero-bias anomaly in quantum wires that were embedded with impurities. The linear conductance G can exhibit cusp features that evolve with the positions of the impurities, and these features can be continuously changed using a combination of spit-gate and top-gate voltages. ZBA is observed regardless of the presence of impurity. Kondo model is inadequate for describing the behaviors of both G and ZBA. Despite the presence of impurity scattering, various ZBA behaviors that resemble those reported in clean quantum wires can be observed. Our results suggest that ZBA is an intrinsic phenomenon in a quantum wire, and its temperature and magnetic field dependence does not pertain to the Kondo correlations in quantum dot. [ABSTRACT FROM AUTHOR]

Highlights • Egg shell membrane template facilitates formation of stabilised b-NiMoO 4 nanowires. • Using egg shell membrane template results in >400% improvement in energy density. • Polymers with chelating functional groups may facilitate access to novel structures. • Electrochemical performance of ESM templated material 6 × greater than no template. Abstract Adding an eggshell membrane (ESM) template to the solution combustion synthesis of NiMoO 4 resulted in the formation of β -NiMoO 4 under mild conditions. It is postulated that the unique nature of the ESM template results in interactions that stabilise this difficult to synthesise form of NiMoO 4. The ESM template led to β -NiMoO 4 particles that were nano-wire like in shape and arranged in an open weave structure that significantly enhanced the mesoporosity and conductance of the material. The specific capacitance was measured as 259 F g−1 in a two electrode system with an energy density of 252.2 W h kg−1. The results indicate that the use of a fibrous like natural polymeric material as a template stabilises materials in preferred crystal forms and shapes leading to much improved electrochemical performance. [ABSTRACT FROM AUTHOR]

We obtain exact expressions for the first three moments of the heat conductance of a quantum chain that crosses over from a superconducting quantum dot to a superconducting disordered quantum wire. Our analytic solution provides exact detailed descriptions of all crossovers that can be observed in the system as a function of its length, which include ballistic-metallic and metallic-insulating crossovers. The two Bogoliubov-de Gennes (BdG) symmetry classes with time-reversal symmetry are accounted for. The striking effect of total suppression of the insulating regime in systems with broken spin-rotation invariance is observed at large length scales. For a single channel system, this anomalous effect can be interpreted as a signature of the presence of the elusive Majorana fermion in a condensed matter system. [ABSTRACT FROM AUTHOR]

A two-dimensional quantum mechanical model is presented for calculating carrier transport in ultra-thin gate-all-around quantum wire transistor (GAAQWT) and carbon nanotube field effect transistor (CNTFET) using coupled mode space approach. Schrödinger and Poisson’s equations are self-consistently solved involving Non-Equilibrium Green’s Function (NEGF) formalism under the ballistic limit along with dissipative effects in terms of self-energy at both the source and drain ends. Effect of structural parameters on drain current, channel length modulation parameter, quantum capacitance, transconductance, subthreshold swing (SS) and drain induced barrier lowering (DIBL) are studied assuming occupancy of only a few lower sub-bands, where comparison is performed taking all other factors, biases and dimensions identical. High-k dielectric (HfO2) independently surrounding the quantum wire (GaAs) and carbon nanotube shows higher drain current and transconductance for GAAQWT but lower quantum capacitance than that obtained for CNTFET. A smaller variation of CLM for CNFET speaks in favour of it for digital quantum circuit applications, whereas GAAQWT is suitable candidate for low-power applications. Effect of structural parameters is investigated within fabrication limit to analyse the effect on electrical characteristics under lower biasing ranges. [ABSTRACT FROM AUTHOR]

Understanding the process of electron tunneling in chirality-induced single-molecule junctions is imperative for the development of nanoscale switching and artificial nanomotors. Based on the combined non-equilibrium Green's functions formalism and the ground-state density functional theory, we present here the charge transport behavior of chiral gold (7,3) nanowires (NWs) in comparison with various other chiral and achiral 1D gold nanostructures as the principal leads to form stable single-molecule junctions. For σ -saturated alkane chains, we find that the contact potential barriers vary widely with the achiral leads but not with the chiral ones, although a close resemblance exists in the tunneling constants. Lower energy gaps for single-molecule junctions with Au(7,3)NWs ensure better electronic conductance even after allowing for the low thermal loss, due mainly to the close-packed arrangements of atoms with minimum wire tension. Our first - principles quantum transport analysis further suggests that chiral Au(7,3)NWs render higher electronic conductance than chiral gold (5,3) nanotubes (NTs), once bridged by either σ -saturated or π -conjugated molecular moieties. It, however, turns out that asymmetricity in the characteristics of channel formation at the lead-molecule contact remains often associated with chiral Au(7,3)NWs only. [ABSTRACT FROM AUTHOR]

Silicon nanowires (SiNW) are highly sensitive to biomolecules. In some publications, changes of SiNW conductance in relation to their concentration levels are displayed. Upon binding, biomolecule charges change the surface potential and, thereby, the SiNW conductance. We discussed earlier that SiNWs can be regarded as long‐channel, ion‐sensitive field‐effect transistors (ISFETs). The choice of a stable working point is important and defines the SiNW conductance. The common detection principle is based on the shift in threshold voltage. Regardless of conductance change or threshold voltage shift, relative values are related to biomolecule concentrations. However, potentiometric detection suffers from Debye screening of biomolecule charges by counter ions of the test solution. This makes biosensing in physiological buffer solutions difficult if not impossible. In this report, a method for impedance sensing with SiNWs, which was earlier used for ISFET devices is introduced. This method gains comparable results to potentiometric sensing. The change of interface impedance is indirectly linked with the biomolecule charges. In addition, the dielectric property of the interface layer plays an important role. At elevated frequencies, our method can be regarded as an alternative mechanism similar to dielectric spectroscopy at low frequencies. Thereby, Debye screening does no longer dominate the recordings. [ABSTRACT FROM AUTHOR]

We introduce a new concept for the solution-based fabrication of conductive gold nanowires using DNA templates. To this end, we employ DNA nanomolds, inside which electroless gold deposition is initiated by site-specific attached seeds. Using programmable interfaces, individual molds self-assemble into micrometer-long mold superstructures. During subsequent internal gold deposition, the mold walls constrain the metal growth, such that highly homogeneous nanowires with 20–30 nm diameters are obtained. Wire contacting using electron-beam lithography and electrical conductance characterization at temperatures between 4.2 K and room temperature demonstrate that metallic conducting wires were produced, although for part of the wires, the conductance is limited by boundaries between gold grains. Using different mold designs, our synthesis scheme will, in the future, allow the fabrication of complex metal structures with programmable shapes. [ABSTRACT FROM AUTHOR]

We present a theoretical method based on Green's function technique and tight-binding approach as well as harmonic approximation in order to calculate the coherent electronic conductance of an extended poly(p-phenylene) oligomer in the presence of thermal atomic vibrations. We study two proposed mass-spring models for atomic vibrations: one, including rigid benzene rings connected to each other by vibrating bonds; and in another, the bonds along the oligomer vibrate even in the benzene rings. The electron-phonon (e-ph) interaction influences the electron hopping energies linearly with respect to atomic displacements. The model shows that the conductance spectra exhibit some new energy gaps in the presence of e-ph interaction even at zero temperature. The conductance is more affected by e-ph interaction when the atomic vibrations are supposed to be present in the benzene rings. At the edges of the band energy and central gap, the phonon-assisted phenomena can be observed. Generally, the increasing e-ph interaction strength as well as temperature destroys the electronic conductance especially in the resonance region. [ABSTRACT FROM AUTHOR]

Quantitative electrical admittance measurements of diffusive superconductor-normal-metal-superconductor (SNS) junctions at gigahertz frequencies and millikelvin temperatures are reported. The gold-palladium-based SNS junctions are arranged into a chain of superconducting quantum interference devices. The chain is coupled strongly to a multimode microwave resonator with a mode spacing of approximately 0.6 GHz. By measuring the resonance frequencies and quality factors of the resonator modes, the dissipative and reactive parts of the admittance of the chain are extracted. The phase and temperature dependence of the admittance near 1 GHz are compared with theory based on the time-dependent Usadel equations. This comparison allows the identification of important discrepancies between theory and experiment that are not resolved by including inelastic scattering or elastic spin-flip scattering in the theory. [ABSTRACT FROM AUTHOR]

In this paper, germanium nanowires (GeNWs) with different cross-sectional areas are considered as the channel of a cylindrical surrounding gate field effect transistors (CSG-FETs) and the electronic properties of them are calculated through the density functional method and Slater-Koster (SK) tight binding model. The corresponding transistor parameters are obtained using Non-equilibrium Green’s function (NEGF) combined by SK model. We find that SK model predicts the well-nigh same bandgap value compared to meta-GGA-DFT approximation, while GGA-DFT underestimates the value of the bandgap. CSG-GeNW-FETs Transistor figure of merit shows a supreme I on /I off ratio which is equal to 10 12 for one of the considered structures with a circular cross-section. The obtained sub-threshold swing (SS) values for the FETs illustrate an increment trend when the supercell size of the germanium nanowire increases whereas the transconductance and ON-current of the FETs decrease when the GeNW supercell size scales down due to the declining of the density of states and electron transmission spectrum. [ABSTRACT FROM AUTHOR]

A single line of dangling bonds (DBs) on Si(100)-2 × 1:H surface forms a perfect metallic atomic-wire. In this work, we investigate quantum transport properties of such dangling bond wires (DBWs) by a state-of-the-art first-principles technique. It is found that the conductance of the DBW can be gated by electrostatic potential and orbital overlap due to only a single DB center (DBC) within a distance of ~16 Å from the DBW. The gating effect is more pronounced for two DBCs and especially, when these two DB "gates" are within ~3.9 Å from each other. These effective length scales are in excellent agreement with those measured in scanning tunnelling microscope experiments. By analyzing transmission spectrum and density of states of DBC-DBW systems, with or without subsurface doping, for different length of the DBW, distance between DBCs and the DBW, and distance between DB gates, we conclude that charge transport in a DBW can be regulated to have both an on-state and an off-state using only one or two DBs. [ABSTRACT FROM AUTHOR]

Vertical InAs nanowire transistors are fabricated on Si using a gate-last method, allowing for lithography-based control of the vertical gate length. The best devices combine good ON- and OFF-performance, exhibiting an ON-current of 0.14 mA/ \mu \textm , and a sub-threshold swing of 90 mV/dec at 190 nm L G . The device with the highest transconductance shows a peak value of 1.6 mS/ \mu \textm . From RF measurements, the border trap densities are calculated and compared between devices fabricated using the gate-last and gate-first approaches, demonstrating no significant difference in trap densities. The results thus confirm the usefulness of implementing digital etching in thinning down the channel dimensions. [ABSTRACT FROM PUBLISHER]

Ballistic electron transport is a key requirement for existence of a topological phase transition in proximitized InSb nanowires. However, measurements of quantized conductance as direct evidence of ballistic transport have so far been obscured due to the increased chance of backscattering in one-dimensional nanowires. We show that by improving the nanowire-metal interface as well as the dielectric environment we can consistently achieve conductance quantization at zero magnetic field. Additionally we study the contribution of orbital effects to the sub-band dispersion for different orientation of the magnetic field, observing a near-degeneracy between the second and third sub-bands. [ABSTRACT FROM AUTHOR]

First principle calculations of the conductance of gold atomic wires containing chain of 3–8 atoms each with 2.39 Å bond lengths are presented using density functional theory. Three different configurations of wire/electrodes were used. For zigzag wire with semi-infinite crystalline electrodes, even–odd oscillation is observed which is consistent with the previously reported results. A lower conductance is observed for the chain in semi-infinite crystalline electrodes compared to the chains suspended in wire-like electrode. The calculated transmission spectrum for the straight and zig-zag wires suspended between semi-infinite crystalline electrodes showed suppression of transmission channels due to electron scattering occurring at the electrode-wire interface. [ABSTRACT FROM AUTHOR]

The organometallic Ru molecular wires 1–3 Ru(PR3)4(C≡CC5H5N)2 [(PR3)4 = (dppe)2 (1), [P(OMe3)]4 (2), and (dmpe)2 (3)] show significantly higher conductance compared to their organic counterpart, 1,4-dipyridyl butadiyne (4). CV and UV-Vis measurements and DFT calculations suggest that the high-lying HOMOs of the Ru wires are the key factor for the high conductance. [ABSTRACT FROM AUTHOR]

We simulate the electron transport in a vertical bi-layer nanowire in order to study an influence of the lateral confinement's shape on a spin polarization of wire's conductance. The active part of considered quantum wire constitutes a double inverted heterojunction In 0.52 Al 0.48 As / In 0.53 Ga 0.47 As which nanostructure can be fabricated in molecular beam epitaxy process while the lateral confinement potential can be finally formed by means of cleaved overgrowth or surface oxidization methods giving the desired rectangular and smooth lateral confinement. In calculations we take into account interaction between charge carriers using DFT within local spin density approximation. We show that if the magnetic field is perpendicular to the wire axis, the pseudogaps are opened in energy dispersion relation E ( k ) what in conjunction with spin Zeeman shift of spin-up and spin-down subbands may enhance the spin polarization of conductance with reference to a single layer wire. For nanowire with rectangular lateral confinement potential we found that the electron density has two maximums localized at wire edges in each layers. This modificates strongly all magnetosubbands giving up to four energy minimums in lowest subband and considerably diminishes widths of pseudogaps what translates into low maximal spin polarization of conductance, not exceeding 40%. This drawback is absent in wire with smooth lateral confinement. However, in order to gain a large spin polarization simultaneous tuning of magnetic field as well as the Fermi energies in both layers of nanowire are required. [ABSTRACT FROM AUTHOR]

We investigate the electronic structure, spin and transport properties of double quantum wires formed by a symmetric, double quartic-well potential subjected to an in-plane magnetic field by taking into account Rashba and Dresselhaus spin-orbit couplings. The energy dispersion relation of the system is analyzed for different strengths of spin-orbit interactions, magnitude and direction of magnetic field. Our numerical results reveal that the existence of aforementioned parameters modifies strongly the energy band structure, introduces a wave vector dependence to energies and also leads to crossings and anticrossings between subbands. This complex structure of energy dispersion gives rise to the appearance of square-wave like oscillations in the conductance. The spin-orbit couplings, magnetic field, potential profile and Fermi energy of an electron significantly affect the depth and width of conductance steps. Moreover, we found that the competing effect between spin-orbit couplings and magnetic field leaves its marks on the spin texturing. [ABSTRACT FROM AUTHOR]

We performed electronic transport measurements on one-dimensional InAs quantum wires. In sufficiently disordered wires, transport is dominated by Coulomb blockade, and the conductance can be well described by tunneling through a quantum dot embedded between two one-dimensional Luttinger liquid wires. In contrast to previous experiments in other material systems, in our system the conductance difference between peak to valley decreases with decreasing temperature for several consecutive peaks. This phenomenon is theoretically expected to occur only for strongly interacting systems with small Luttinger interaction parameter g < 1/2; we find for our InAs wires a value of g ≈ 0.4. Possible mechanisms leading to these strong correlations are discussed. [ABSTRACT FROM AUTHOR]

We have studied the origin of the electron energy relaxation in clean single channel quantum wires, accounting for the scattering processes that involve threee particule collisions. Thermal transport of Single-channel quantum wires, where a lower value of the thermal conductance than that predicted by the wiedemann-Franz law as observed at the plateau of the electrical conductance. Momeutum resolved tunneling spectroscopy provided direct evidence for the electronic thermalisation in one dimensional systems. Interaction effects are responsible for the observed features. Fabrication of tunable constrictions in high mobility two-dimensional electron gases have allowed precise and sensitive thermal measurements in clean one dimensional systems. We have found that the thermal conductance is reduced by interactions, which is qualitatively consistent with the experimental observation. The three particle collisions are responsible for relaxation and provide an explicit solution of the Boltz-Mann equation. Electrons maintain their integrity during collisions and thus neglects effects of spin-charge separation. The effects of electron-electron collisions on the distribution function depends strongly on the length of the wire. Short wires are traversed by the electrons relatively fast. In the limit of a very long wire we found full equilibration of left and right moving electrons into a single distribution. [ABSTRACT FROM AUTHOR]

The transport properties of Ge-doped single GaN nanowires are investigated, which exhibit a weak localization effect as well as universal conductance fluctuations at low temperatures. By analyzing these quantum interference effects, the electron phase coherence length was determined. Its temperature dependence indicates that in the case of highly doped nanowires electron-electron scattering is the dominant dephasing mechanism, while for the slightly doped nanowires dephasing originates from Nyquist-scattering. The change of the dominant scattering mechanism is attributed to a modification of the carrier confinement caused by the Ge-doping. The results demonstrate that the phase coherence length can be tuned by the donor concentration making Ge-doped GaN nanowires an ideal model system for studying the influence of impurities on quantum-interference effects in mesoscopic and nanoscale systems. [ABSTRACT FROM AUTHOR]

We study the conductance renormalization for the four-lead junction of semi-infinite wires in the scattering state formalism. We use the model of spinless fermions with a short-range Luttinger-type interaction and find the renormalization group (RG) equations for the conductances of the system in the first order of the fermionic interaction. In contrast to the well-known cases of two-lead and three-lead junctions, the four-lead case does not admit a formulation of the RG equations solely in terms of conductances. The arising ambiguity with arbitrariness in the choice of the sign of S-matrix elements related to identical conductance matrices might be connected with a symmetry of the particle-hole type in the Hamiltonian. We show that there are two distinct RG flows from any initial point in the space of conductances. The discovered ambiguity does not affect the scaling exponents at the fixed points. [ABSTRACT FROM AUTHOR]

Making a combined use of bosonization and fermionization techniques, we build nonlocal transformations between dual fermion operators, describing junctions of strongly interacting spinful one-dimensional quantum wires. Our approach allows for trading strongly interacting (in the original coordinates) fermionic Hamiltonians for weakly interacting (in the dual coordinates) ones. It enables us to generalize to the strongly interacting regime the fermionic renormalization group approach to weakly interacting junctions. As a result, on one hand, we are able to pertinently complement the information about the phase diagram of the junction obtained within the bosonization approach; on the other hand, we map out the full crossover of the conductance tensors between any two fixed points in the phase diagram connected by a renormalization group trajectory. [ABSTRACT FROM AUTHOR]

We have proposed a feasible scheme to detect the Majorana fermions via a triple quantum-dot structure coupled a normal-metal lead and a Majorana nanowire. Our results show that the conductance spectrum display the clear Dicke-like effect, and the increase of the coupling strength between the central dot and the quantum nanowire can enhance the pronounced property. The nonzero Majorana level induce the split of the conductance peak, the dip with zero value is permanently pinned at the zero Fermi level, we find that the conductance spectrum exhibit the symmetrical feature with respect to the energy levels of two side quantum dots, and the strong coupling coefficient can reduce the region of the zero conductance. Moreover, the current-noise Fano factor can approach 2 at low bias and the large Majorana level due to the Majorana-assisted resonant transport, the significant dips of the Fano curve also indicate the coherent oscillations resulting from the nonzero Majorana level. These results are expected to serve as a sensitive indication for the detection of the Majorana bound states. [ABSTRACT FROM AUTHOR]

Ninety-eight one-dimensional channels defined using split gates fabricated on a GaAs/AlGaAs heterostructure are measured during one cooldown at 1.4 K. The devices are arranged in an array on a single chip and are individually addressed using a multiplexing technique. The anomalous conductance feature known as the "0.7 structure" is studied using statistical techniques. The ensemble of data shows that the 0.7 anomaly becomes more pronounced and occurs at lower values as the curvature of the potential barrier in the transport direction decreases. This corresponds to an increase in the effective length of the device. The 0.7 anomaly is not strongly influenced by other properties of the conductance related to density. The curvature of the potential barrier appears to be the primary factor governing the shape of the 0.7 structure at a given T and B. [ABSTRACT FROM AUTHOR]

A unified theory for the conductance of an infinitely long multimode quantum wire whose finite segment has randomly rough lateral boundaries is developed. It enables one to rigorously take account of all feasible mechanisms of wave scattering, both related to boundary roughness and to contacts between the wire rough section and the perfect leads within the same technical frameworks. The rough part of the conducting wire is shown to act as a mode-specific randomly modulated effective potential barrier whose height is governed essentially by the asperity slope. The mean height of the barrier, which is proportional to the average slope squared, specifies the number of conducting channels. Under relatively small asperity amplitude this number can take on arbitrary small, up to zero, values if the asperities are sufficiently sharp. The consecutive channel cut-off that arises when the asperity sharpness increases can be regarded as a kind of localization, which is not related to the disorder per se but rather is of entropic or (equivalently) geometric origin. The fluctuating part of the effective barrier results in two fundamentally different types of guided wave scattering, viz., inter- and intramode scattering. The intermode scattering is shown to be for the most part very strong except in the cases of ( a ) extremely smooth asperities, ( b ) excessively small length of the corrugated segment, and ( c ) the asperities sharp enough for only one conducting channel to remain in the wire. Under strong intermode scattering, a new set of conducting channels develops in the corrugated waveguide, which have the form of asymptotically decoupled extended modes subject to individual solely intramode random potentials. In view of this fact, two transport regimes only are realizable in randomly corrugated multimode waveguides, specifically, the ballistic and the localized regime, the latter characteristic of one-dimensional random systems. Two kinds of localization are thus shown to coexist in waveguide-like systems with randomly corrugated boundaries, specifically, the entropic localization and the one-dimensional Anderson (disorder-driven) localization. If the particular mode propagates across the rough segment ballistically, the Fabry–Pérot-type oscillations should be observed in the conductance, which are suppressed for the mode transferred in the Anderson-localized regime. [ABSTRACT FROM AUTHOR]

Various optimized Si and its alloy nanowires, from a monoatomic chain to helical and multishell coaxial cylinder, have been obtained. Results reveal that the structure of the Si nanowires transforms as the radii of the carbon nanotubes increase, despite of the chirality of the CNTs. We also calculate the physical properties, such as density of states, transmission functions, current–voltage ( I – V ) characteristics, and conductance spectra ( G – V ) of optimized nanowires and alloy nanowires sandwiched between two gold contacts. Interestingly, compared with the pure Si nanowires, the conductance of the alloy nanowires is even lower. [ABSTRACT FROM AUTHOR]

Wemodel a core–shell nanowire (CSN) by a cylindrical surfaceof finite length. A uniform magnetic field perpendicular to the axisof the cylinder forms electron states along the lines of zero radialfield projection, which can classically be described as snaking states.In a strong field, these states converge pairwise to quasidegeneratelevels, which are situated at the bottom of the energy spectrum. Wecalculate the conductance of the CSN by coupling it to leads and predictthat the snaking states govern transport at low chemical potential,forming isolated peaks, each of which may be split in two by applyinga transverse electric field. If the contacts with the leads do notcompletely surround the CSN, as is usually the case in experiments,the amplitude of the snaking peaks changes when the magnetic fieldis rotated, determined by the overlap of the contacts with the snakingstates. [ABSTRACT FROM AUTHOR]

The strongly temperature-dependent ionic mobility in polymer electrolytes is used to 'freeze in' specific ionic charge environments around a nanowire using a local wrap-gate geometry. This makes it possible to set both the threshold voltage for a conventional doped substrate gate and the local disorder potential at temperatures below 220 K. These are characterized in detail by combining conductance and thermovoltage measurements with modeling. The results demonstrate that local polymer electrolyte gates are compatible with nanowire thermoelectrics, where they offer the advantage of a very low thermal conductivity, and hold great potential towards setting the optimal operating point for solid-state cooling applications. [ABSTRACT FROM AUTHOR]

We consider electronic transport through semiconducting nanowires (W) with spin-orbit interaction (SOI), in a hybrid N-W-N setup where the wire is contacted by normal-metal leads (N). We investigate the conductance behavior of the system as a function of gate and bias voltage, magnetic field, wire length, temperature, and disorder. The transport calculations are performed numerically and are based on standard recursive Green's function techniques. In particular, we are interested in understanding if and how it is possible to deduce the strength of the SOI from the transport behavior. This is a very relevant question since so far no clear experimental observation in that direction has been produced. We find that the smoothness of the electrostatic potential profile between the contacts and the wire plays a crucial role, and we show that in realistic regimes the N-W-N setup may mask the effects of SOI, and a trivial behavior with apparent vanishing SOI is observed. We identify an optimal parameter regime, with neither too smooth nor too abrupt potentials, where the signature of SOI is best visible, with and without Fabry-Perot oscillations, and is most resilient to disorder and temperature effects. [ABSTRACT FROM AUTHOR]

Transport properties of free-standing ultrathin pristine and alloyed nanowires of noble metals (Ag, Au, Cu, Pt, AgAu, AgCu, AgPt, AuCu, AuPt and CuPt) with various topologies (linear, ladder and double zigzag (DZZ)) have been studied using non-equilibrium Green’s function (NEGF) technique, based on density functional theory (DFT) as implemented in TranSIESTA. Compared to pristine nanowires of linear topology (Ag, Au, Cu and Pt), corresponding alloyed nanowires show diffusive/non-ballistic conductance, a result of decrease in mean free path on alloying. However, pristine and alloyed nanowires of ladder and DZZ (DZZ1, DZZ2 and DZZ3) topologies are found to show ballistic behaviour, a consequence of increase in coordination number as one moves from linear to ladder and finally DZZ topology, leading to increased mean free path and hence ballistic transport. For all the studied topologies of pristine metallic nanowires the current generally increases linearly with the V bias . However, the possibility of NDC (negative differential conductance) effect of alloyed nanowires has been observed. The I – V characteristics of the AgPt nanowires with linear and DZZ1 topologies; CuPt nanowires of all the topologies; AuPt nanowires with DZZ1 and DZZ2 topologies and AgPt nanowire with DZZ1 topology are found to show tunnel diode like characteristic. [ABSTRACT FROM AUTHOR]

We study interaction-induced backscattering in clean quantum wires with adiabatic contacts exposed to a voltage bias. Particle backscattering relaxes such systems to a fully equilibrated steady state only on length scales exponentially large in the ratio of bandwidth of excitations and temperature. Here we focus on shorter wires in which full equilibration is not accomplished. Signatures of relaxation then are due to backscattering of hole excitations close to the band bottom which perform a diffusive motion in momentum space while scattering from excitations at the Fermi level. This is reminiscent to the first passage problem of a Brownian particle and, regardless of the interaction strength, can be described by an inhomogeneous Fokker-Planck equation. From general solutions of the latter we calculate the hole backscattering rate for different wire lengths and discuss the resulting length dependence of interaction-induced correction to the conductance of a clean single channel quantum wire. [ABSTRACT FROM AUTHOR]

Electrochemical studies are reported on a series of peptides constrained into either a 310-helix (1-6) or β-strand (7-9) conformation, with variable numbers of electron rich alkene containing side chains. Peptides (1 and 2) and (7 and 8) are further constrained into these geometries with a suitable side chain tether introduced by ring closing metathesis (RCM). Peptides 1, 4 and 5, each containing a single alkene side chain reveal a direct link between backbone rigidity and electron transfer, in isolation from any effects due to the electronic properties of the electron rich side-chains. Further studies on the linear peptides 3-6 confirm the ability of the alkene to facilitate electron transfer through the peptide. A comparison of the electrochemical data for the unsaturated tethered peptides (1 and 7) and saturated tethered peptides (2 and 8) reveals an interplay between backbone rigidity and effects arising from the electron rich alkene side-chains on electron transfer. Theoretical calculations on β-strand models analogous to 7, 8 and 9 provide further insights into the relative roles of backbone rigidity and electron rich side-chains on intramolecular electron transfer. Furthermore, electron population analysis confirms the role of the alkene as a stepping stone for electron transfer. These findings provide a new approach for fine-tuning the electronic properties of peptides by controlling backbone rigidity, and through the inclusion of electron rich side-chains. This allows for manipulation of energy barriers and hence conductance in peptides, a crucial step in the design and fabrication of molecular-based electronic devices. [ABSTRACT FROM AUTHOR]

Thermal transport through profiled and abrupt contacts between a nanowire and a reservoir has been investigated by thermal conductance measurements. It is demonstrated that above 1K the transmission coefficients are identical between abrupt and profiled junctions. This shows that the thermal transport is principally governed by the nanowire itself rather than by the resistance of the thermal contact. These results are perfectly compatible with the previous theoretical models. The thermal conductance measured at sub-Kelvin temperatures is discussed in relation to the universal value of the quantum of thermal conductance. [ABSTRACT FROM AUTHOR]

The properties of conductance in one-dimensional (1D) quantum wires are statistically investigated using an array of 256 lithographically identical split gates, fabricated on a GaAs/AlGaAs heterostructure. All the split gates are measured during a single cooldown under the same conditions. Electron many-body effects give rise to an anomalous feature in the conductance of a one-dimensional quantum wire, known as the "0.7 structure" (or "0.7 anomaly"). To handle the large data set, a method of automatically estimating the conductance value of the 0.7 structure is developed. Large differences are observed in the strength and value of the 0.7 structure [from 0.63 to 0.84×(2e²/h)], despite the constant temperature and identical device design. Variations in the 1D potential profile are quantified by estimating the curvature of the barrier in the direction of electron transport, following a saddle-point model. The 0.7 structure appears to be highly sensitive to the specific confining potential within individual devices. [ABSTRACT FROM AUTHOR]

Abstract: A large progress in pH sensing with nanowire based ion-sensitive field-effect transistors (ISFETs) has been demonstrated over the years. The electrochemical reactions occurring at the wire surface-to-electrolyte interface play a key role in the detection of ions. In this letter, we show that pH sensing can also be performed on dried samples, through electrical measurements in air with a new kind of memristive sensor. The detection of different concentrations of [H+] is confirmed by both the increased conductance and hysteretic voltage gap of the wires. The observed change in the electrical properties with pH in dry conditions is related to the formation of a wet film at the nanowire surface. Ions from the initial solution are free to move in the final water thin film at the sensing interface with consequent polarization of the NW surface. [Copyright &y& Elsevier]

A system with an interacting quantum dot side-coupled to a wire is analyzed. Transport through the quantum wire is studied using the equation of motion method. It was shown that the conductance (transmission) provides a suppression due to the destructive interference effects. The one dip, and two dips structure of the conductance is obtained for large and for moderate Coulomb repulsion. [ABSTRACT FROM AUTHOR]

We present an extensive experimental and theoretical study of the proximity effect in InAs nanowires connected to superconducting electrodes. We fabricate and investigate devices with suspended gate-controlled nanowires and nonsuspended nanowires, with a broad range of lengths and normal-state resistances. We analyze the main features of the current-voltage characteristics: the Josephson current, excess current, and subgap current as functions of length, temperature, magnetic field, and gate voltage, and compare them with theory. The Josephson critical current for a short-length device, L = 30 nm, exhibits a record high magnitude of 800 nA at low temperature that comes close to the theoretically expected value. The critical current in all other devices is typically reduced compared to the theoretical values. The excess current is consistent with the normal resistance data and agrees well with the theory. The subgap current shows a large number of structures; some of them are identified as subharmonic gap structures generated by multiple Andreev reflection. The other structures, detected in both suspended and nonsuspended devices, have the form of voltage steps at voltages that are independent of either the superconducting gap or length of the wire. By varying the gate voltage in suspended devices, we are able to observe a crossover from typical tunneling transport at large negative gate voltage, with suppressed subgap current and negative excess current, to pronounced proximity junction behavior at large positive gate voltage, with enhanced Josephson current and subgap conductance as well as a large positive excess current. [ABSTRACT FROM AUTHOR]

A single molecular resistive (conductance) switch via control of anchoring positions was examined by using a molecule consisting of more than two same anchors. For this purpose, we adopted the covered quaterthiophene (QT)-based molecular wire junction. The QT-based wire consisted of two thiophene ring anchors on each side; thus, shift of anchors was potentially possible without a change in the binding modes and distortion of the intramolecular structure. We observed three distinct conductance states by using scanning tunneling microscope-based break junction technique. A detailed analysis of the experimental data and first-principles calculations revealed that the mechanism of the resistive switch could be explained by standard length dependence (exponential decay) of conductance. Here, the length is the distance between the anchoring points, i.e., length of the bridged π-conjugated backbone. Most importantly, this effective tunneling length was variable via only controlling the anchoring positions in the same molecule. Furthermore, we experimentally showed the possibility of a dynamic switch of anchoring positions by mechanical control. The results suggested a distinct strategy to design functional devices via contact engineering. [ABSTRACT FROM AUTHOR]

Highlights: [•] Terminal connection affects electron transport greatly. [•] Quantum interference in conjugated molecules. [•] Structure features of well conductive molecular wires. [•] Conductance drops first then rises as the molecular length increases. [•] Phenyl rings in a conjugated system controls the molecular orbital levels. [ABSTRACT FROM AUTHOR]

We grow a tiled structure of insulating two-dimensional LaAlO3/SrTiO3 interfaces composed of alternating one and three LaAlO3 unit cells. The boundary between two tiles is conducting. At low temperatures this conductance exhibits quantized steps as a function of gate voltage indicative of a one-dimensional channel. The step size of half the quantum of conductance is evidence for the absence of spin degeneracy. [ABSTRACT FROM AUTHOR]

The Kitaev quantum wire (KQW) model with open boundary possesses two Majorana edge modes. When the local chemical potential on a defect site is much higher than that on other sites and than the hopping energy, the electron hopping is blocked at this site. We show that the existence of such a defect on a closed KQW also gives rise to two low-energy modes, which can simulate the edge modes. The energies of the defect modes vanish to zero as the local chemical potential of the defect increase to infinity. We develop a quantum Langevin equation to study the transport of KQW for both open and closed cases. We find that when the lead is contacted with the site beside the defect, we can observe two splitted peaks around the zero-bias voltage in the differential conductance spectrum, whereas if the lead is contacted with the bulk of the quantum wire far from the the defect or the open edges, we cannot observe any zero-bias peak. [ABSTRACT FROM AUTHOR]